Yet another Wildstar topic ... but slightly different :)

I would pick GW2 as a free option.More ppl/more updates/has provided lots so far
On the other hard wildstar has end game/GW2 has now will have endgame content i think
As for WoW it clearly provides the best enterntainment and constant updates but at a cost
Keep in mind that mmo's are clearly more enjoyable when played with friends of normal+IQ.

Guild wars 2 is generally more polished and better in almost every way - though it depends what do you want to do in MMO.
What I didn't like about Wildstar the most is their engine, its really badly optimised and clunky, still many problems with it that weren't fixed since launch and propably never will - random fps drops, UI freezing etc etc.
To make it easier for you:
If you want to pvp - Guild Wars 2 is the best choice, frequent balance patches, they do invest quite a bit of resource into pvp side of things, currently lack of endgame other than pvp/collecting costumes, raids propably coming but you need to buy expansion for them.
Raids - Wildstar has definitely more pve content than guild wars 2 atm, haven't raided myself but heard the ones in wildstar are pretty hard, ie one person getting a dc and you basically have to start over, but again I dont like the poor engine, completely ruins it for me (though if you have some super good computer it might be fine for you)
Another option I would propose is Rift, quite decent pve and pretty easy entry into raids. Raids themselves are rather easy except the newest tier that always gets nerfed after couple months. Recently Trion is doing some questionable decisions though with the way they are monetising the game
(a lot of classes behind paywall, economy is crap) PvP in Rift is garbage, pve is dcent.

Tl;dr
If you want to pvp GW2, hard raids and have high end pc Wildstar, easier raids Rift

The problem is that i was a WoW subscriber since vanilla, and i dropped right after the Pandaria expansion. Got myself into GW2 alone, doing jumping puzzles, pve but when it came to pvp ... it was chaotic ... well ... i was mostly interested in the world pvp. And after some time i got bored with all the cosmetics and eyecandy. Now i just want a casual MMO which doesn't hit me with the paywall after i play is for 1-2 months. Overall, i heard that Wildstar has a very good payment model ... and if you grind long enough you could buy every single thing in the store, like character slots, inventory/bank slots, etc. Is that right?

I've been playing Guild Wars 2 since xmas 2012, all though not as avidly over the past several months, but I have been slowly getting back into it properly (other than just signing in every day to get the dailies) due to the new expansion coming out on Oct 23rd. I just bought the expansion and have participated in the beta weekend this last weekend and it looks like I will definitely enjoy it going forward. If you have not bought the expansion then maybe playing Wildstar will be better for you as a lot of the stuff for GW2 will be locked behind that expansion pay wall essentially (ie new story content and areas).

I had a 1 month sub (from the e3 Humble Bundle) for Wildstar which I activated on Novmeber 1st. It was my plan to play it until the end of November then quit. I am still playing it as I never had as much time as I wanted to at least fully level one character, however I would say it is vastly different to GW2. I personally am not that big a fan of the combat compared to GW2, as it feels less fluid, slower, and I spend more time looking at the aoe ground target than I do at looking at what I am actually doing, which can be frustrating, but a lot of people do like it. The storyline (at least for Dominion) and the way it plays out is all over the place and hard to follow, but I enjoyed exploring the first few areas at least, as it has some fun things to explore and find out if you are into that kind of thing outside of just doing the Regional and World Story quests. I personally am not going to get really into the complexity of the crafting system, rune system, and gearing and making the perfect build for end game as I plan on just enjoying the story and leveling up and exploring the areas. I don't plan on investing any money into the game. Like GW2's f2p model its is mainly extra quality of life features you will miss out on, like a few extra character slots, bag space etc. My account now has become f2p, and I am steadily getting these "omnibits" that can be used to purchase extra things, however I probably won't even bother. I've never felt the need to use the auction house/trading post, and the f2p lets you play the entire game. So I would say you could at least try it out and see if you enjoy the art style, combat, and leveling mechanism out.

On a plus note, the HOUSING in itself is absolutely amazing, and worth making a f2p account for just to fudge around with the housing system. Coming from GW2 it is also nice to be able to use mounts.

TL:DR
IMHO I would recommend any MMO fan make a f2p account on Wildstar and level to at least lvl15, this will basically let you know if you like the art style/graphics, story, classes/combat systems, lvl'ing/gear systems, and be able to explore at least 2 areas. You will also be able to have fun with the housing system. After that you can judge whether it is worth investing any more time into it. Investing money into the game is purely for cosmetic or quality of life improvements.

At least F2P model wise Wildstar is among the most generous. No race, class, or content locks and the premium currency can drop from anything. Ive been playing semi casually, am lvl 25, and already have enough for another character slot if want it. I think only 2 game affecting things from paying really, 1 is something like 5% higher xp and rep from sub and the other is buying more rune slots for gear. Both of which can be bought from earning premium currency (omnibits) from playing and from login rewards. So from what I understand no reason cannot be equal to someone who paid alot.

GW2 the trial is ok, certainly constrained but enough to demo (like WoW starter version), if own it they are certainly generous although inconsistant and often seemingly without focus. They have added so many things over the years that they said would be a base to build on just to never look at it again. Usually it feels like 75% is meh, then once in awhile they do something that really shows you the potential which keeps you hoping til the next time. Few examples off top of head would be SAB, Marionette, Invasion of Southsun (in concept if not execution due to server issues), Razing of LA, Bazaar of the Four Winds, Halloween, Glint's Lair, and Queen's Gauntlet/Jubilee.

It is not fair to compare the two though, they are very different beasts only sharing active combat and open world MMO traits. GW2 have seen called the tourist or perfect teritary MMO, it was built for hopping in and out at a whim and just doing whatever feel like. Due to this and how easy progression is it also pairs well with more standard MMOs like WoW, FF, and Wildstar. Can log on and have a good time just going site seeing for 30 minutes, and even get a level purely from the discovering XP.

GW2 cannot be played like any other MMO or you will get bored fast it is very much stop and smell the roses. Listen to npcs, look into caves for hidden stuff, ect. While Wildstar at it's core is the same breed as WoW or Rift and a throwback in some ways and a modernization in others but overall with a bright style covering quite a bit of darkness. In some ways the two MMOs are complementary.

Movement and combat both feel good, but are different takes on the similar style, that seen Wildstar does have alot of hidden stuff but not as much as GW2 which is important factor to me. I also got some bias in that I love the mesmer and projectile reflect, which is somewhat GW2 exclusive. There is a QoL feature in Wildstar I wish GW2 would adopt, mouselook mode which is standard most anywhere with active combat. Right now only way to get it is use an outside addon, which might put your account at risk.

TL;DR
Overall I would just say try both and keep an open mind they are different beasts but somewhat complementary, For example many right now in Wildstar are playing it while waiting for GW2 expansion to come later this month.