New XCOM or old?

The new one is nice looking, but dumbed down pretty badly. If you want something you can get thought quickly then the new one is best.The old one requires more time and managment, both in ground combat and in base managment. Old one allows for more options during combat, more equipment, more shot types, more stances, more... alot of things lol. New one has some special abilites your units learn as they get promoted. If you dont have anything against playing old games and like more micro managing in games, then get the original and wait until the new one dropps right down in price.

New one is dumbed down pretty badly, but i did enjoy it. :3

Having not actually played X-COM Classic my opinion isn't very informed, but I would say that XCOM:EU is a very, very good game. But it's very approachable, which will clash with your expectations. I imagine that in many respects Dark Souls feels more like a X-COM game should than new XCOM:EU does. It had the sense of mystery, dread, and terrible magnificence that XCOM:EU lost for me when I managed to start farming the aliens for materials.

Also I personally take any claim of 'dumbing down' with copious amounts of salt. "Civ V is dumbed down." "DA2 is dumbed down." "Skyrim is dumbed down." I would say no they aren't. They're streamlined, simplified, yes. But in many respects they're distillations of what made their predecessors work (some more/less successful than others). This may make them weaker yes, but the core appeal still hasn't been lost.

If you want real dumbing down, look no further than Deus Ex: Invisible War. 10% of the depth of the original, 100% of the magic lost.

i'm looking forward for xenonauts, but it's taking loong..

While the new one is technically easier, unless you like old-style game difficulties, the original is fucking hard.

yeah the original wasnt very fun to me and i didnt like it too difficult, i got enemy unknown and i love it, awesome game tons of replayability and its not too easy

The combat in the new one is more focused, requires more tactical analysis during battles due to the smaller squad size and the smaller maps. Losing a soldier in the new one is a much bigger deal than losing one in the older one.

The older XCOM has a much steeper learning curve, since you're pretty much thrown into being a full-fledged commander without any kind of tutorials, plus there are more options to make your life more difficult in your strategic management of the bases. Some of the additional things you have to manage can be kind of tedious, such as making sure everyone's carrying the right types of ammo and that there's enough for everyone before every battle. In the new one you can pretty much jump straight into combat with minimal micromanagement.

The older one gives you more control in almost every aspect of the game, from base-building to UFO interception to ground combat. One of the features I miss in the new one is the ability to aim at walls and obstacles to destroy them and make new entry points or allow for another member of the squad to take a clean shot by taking down the alien's cover.

They're both fun. I prefer the older one, since there are some things that irk me in the newer one, such as the limited control and the free movement the aliens get every time you spot them - once I even lost a battle before any shots were fired after moving my last guy only to release a group of chrysalids (really nasty alien species) that then proceeded to surround my men without me being able to fire back. It's still a fun game though, the battles are often quite intense.

Also a very similar style game that might interest you UFO: Afterlight is pretty good (a bit older and often on sale).

But as to your question, I never played the classic so I can only say that the new XCOM was a great game. Also the new one has a free demo and might be worth trying out (it's a fairly short demo though).

imho, depends on how much time and patience you have.
I haven't played the new one just yet, but I've put a few hours into the old one and also played a demo of the old one back in the 90s.
When people say it's hard and about micromanaging and you see the levels that you fight on and you're thinking, "okay, cool -- I like it when it's difficult, I think I can do that! It'll be fun!" You're missing half the game. The base management, around the globe, multiple bases, and all the research projects and personnel management those bases carry out, and all the nations panicking and having to decide which ones you need to save to get enough funding, and then realizing that the layout of your bases is important, and trying to chase UFOs you can't detect yet, etc., etc., etc.
The game is hard. But if you do have the patience for it, it is a lot of fun. I'd suggest either looking up gameplay on YouTube or downloading the old DOS demo (which, IIRC, really only focuses on the combat) to get a better sense of the game.

The original Xcom is a great game, and Terror from the Deep is pretty good, but everything after that is pretty meh. The new one though is a pretty dang good game. I was expecting to not like it as much due to the many many changes, but it's a very well done revamp.

Positives for original 2 games - Genuinely thrilling, lot of micro managing and complex decision making. Brutally hard on hardest difficutly. Lots of replayability (sequence of events is mostly different every time you play), generally good AI.
Negatives - Arduous, frustrating RNG

Xcom Enemy Unknown is quite enjoyable until you start playing on Classic and Impossible difficulty. Those modes are pretty cheesy and the CPU is horrendously cheating, those modes are a pain to deal with. And Impossible is what the mode says, almost Impossible to beat.

The new one is a bit different game than the original one but it's really cool and it's like the only turn based squad tactics game that's come out in years so it's definitely worth playing.

New XCOM

Dumbed down? No. Made for a modern gamer? Yes.

XCOM EU definitely, I recommend play it in Classic difficulty with Ironman mode on.
P.S: I didn't play the old ones