Which are the best visual novels on steam?

both are free
http://store.steampowered.com/app/331470/ ,one of my favourite VN,spent about 25-30 hours to get all the endings,there are also mods made by players
http://store.steampowered.com/app/367120/ i really enjoyed this one,it' has english voice acting,and amazing bloopers

this looks quite good http://store.steampowered.com/app/349300/

Games by Telltale
Eden*
Maybe "To the Moon"
And "Everlasting Summer" (Russian work). It's available in English and free.

Long Live The Queen http://store.steampowered.com/app/251990/

Higurashi

Hmm, I think those I liked most (Higurashi, Magical Diary, Cinders, Long Live the Queen) have already been mentioned, so:
X-note and Train of Afterlife are decent, though short and require a walkthrough
Nameless and Dandelion should be good (I only played Nameless for a bit though)
Hunie Pop is more of a match 3 but it's quite fun XD

Clannad is, apparently, coming out on Steam at some point, and that's one of the most classic classics out there.

Any good VN where the characters have regular-sized eyes (and preferably not build using RPGMaker)?

none of them, theyre all censored

None.

http://www.pcgamer.com/kindred-spirits-on-the-roof-is-bringing-frank-depictions-of-sex-to-steam/

Also Juniper Knot, not sure if it's on Steam like their other VN but it's free
http://dischan.co/product.php?productID=4

http://store.steampowered.com/app/397270 this looks promising ... ( ͡° ͜ʖ ͡°) well i didnt play many VNs so thats what id pick if id have to buy one

Kepe in mind before reading this that I haven't played every single VN there is on steam, cause that's gonna take a long time with a backlog of 1,000+ games. So, no, I haven't played Analogue or Fruit of Grisaia. Also, I am several days late in posting this comment, mostly due to laziness. Links to the store pages will be available, if you decide to buy them.

Anything developed/published by Winter Wolves - http://store.steampowered.com/search/?publisher=Winter%20Wolves : I can't really decide if these are even Visual Novels, or if they're just Dating Sims that might resemble a VN. For example, the 3 Heileen games that exist can be considered VNs, cause they're just VNs. Games like Always Remember Me, however, aren't VNs at all, just Dating Sims. So, yeah, Winter Wolves confuses me in that regard.

Princess Evangile - http://store.steampowered.com/app/344630/ : Keeping in mind the fact that I haven't played through Fruit of Grisaia yet, I can easily say I think its the best VN on steam. Helps that the Princess Evagile W Happiness fandisk, or basically "Princess Evangile with extra routes for other characters and after stories for characters who already have routes in the original release" was recently confirmed to be released on steam (And Mangagamer's site).

Everlasting Summer - http://store.steampowered.com/app/331470/ : OH GOD I really hate this game with a passion. The art style was ugly, to say the least, that card tournament minigame was the one element of gameplay I hated most, being unable to figure out how to play it since I was skipping through never-ending text when the instructions came up (Especially so since its crucial to 100%ing the game, as you need to win/lose that card tournament for several routes), the communism themes didn't really sit well with me, and yes, Hatsune Miku's a character in this game, with her own route and everything. No wonder why I hate the game they have on greenlight right now... http://steamcommunity.com/sharedfiles/filedetails/?id=510315215

Also, btw, you know how, when you boot up the game, you get a message that informs you that all the characters in this VN are aged 18+? There is no possible way Ulyana can be 18 years old, judging by her appearance in the game.

Snow Light - http://store.steampowered.com/app/329480/ : Never played this before. so not as bad as Everlasting Summer (I suppose?), but still pretty bad. And its the only Visual Novel I own that costs $100.

If My Heart Had Wings - http://store.steampowered.com/app/326480/ : I really wanted to like this game, I really did. It's ultimately the unneeded censorship (No kissing scenes? Really? H-scenes I can understand, but scenes where 2 characters just kiss?) and the graphical glitches that tend to happen on background images (Then again, this game and a Windows 8 Laptop isn't a good combination) every now and then killed it for me.

Hatoful Boyfriend - http://store.steampowered.com/app/310080/ : Given, it does have a pretty weird concept (Pigeons), but turns out to be pretty good when you play it. Or, as they say, "A better love story than Twilight".

Nekopara - http://store.steampowered.com/search/?developer=NEKO%20WORKs : Its just a cute story about 2 catgirls, which can be a welcome relief after playing through a depressing VN or something. Again, chest bounciness sliders.

Sakura series - http://store.steampowered.com/search/?developer=Winged%20Cloud : Let's face it, the only reason people buy Sakura games anymore is because of the fanservice featured in the Sakura games. Don't expect a coherent story, it's just fanservice nowadays.

Narcissu - http://store.steampowered.com/app/264380/ : Its a pretty old game, but it's pretty depressing (Teh feels), and its free, so go for it. I recommend playing Narcissu 2nd before Narcissu 1st cause Narcissu 2nd is actually a prequel to Narcissu 1st.

Planetarian - http://store.steampowered.com/app/316720/ : If you ever watched anime, you'd know what Key is (Think: Angel Beats, Clannad). Yes, they made this game. BUY IT.

Katawa Shoujo - http://www.katawa-shoujo.com/ : I never really could get immersed into this visual novel. I can see why others like it, but it wasn't my cup of tea...

eden* and narcissu are my recommendations. I've written quite long reviews for both here http://steamcommunity.com/id/zeroxxx/recommended/315810

and here: http://steamcommunity.com/id/zeroxxx/recommended/264380

I know at least some of these have been mentioned already, but most of 'em deserve mentioning again, I think!

Analogue: A Hate Story
Blue Rose
Go! Go! Nippon! My First Trip to Japan
Home
Long Live the Queen
Sakura Spirit
Soul Gambler
Sunrider: Mask of Arcadius

There are some pretty good one on steam.
The Fruit of Grisaia
If My Heart Had Wings
Higurashi When They Cry (i still need to get this one for myself)

and /vg/ makes lists of good visual novels for people who are trying to get into them Link here i would recommend a good amount on this list as i have read most of them and they haven't steered me wrong yet.
one that i would recommend and seems have been recommended before is Katawa Shoujo. really good was my first read and what got me into VN's

I recently played this short, but well made free visual novel and enjoyed:
The Average Everyday Adventures of Samantha Browne
A nice story experience, can be harder to complete, but then has a guide if not succeed or frustrate. :D

Zero Time Dilemma is the best visual novel on Steam, but it's also the third game in a trilogy that absolutely needs to be played in order. I don't even recommend looking at the store page until you've played the first two.

They've announced that the first two games are on the way, so keep an eye peeled for 9 Hours, 9 Persons, 9 Doors and pick that up when it comes out.