Wow, these are some rough matchups.
Lost Pig is of course a classic and many people’s early introduction to IF, notable for a very well developed PC and NPC, while Suveh Nux has a real analytics and logically satisfying puzzle style.
Superluminal Vagrant Twin is very accessible, has a nice grind loop and is very nonlinear, with tons to do. Excalibur has a unique format (fake wiki) and a lot of layers. Both have excellent world building.
A Long Way to the Nearest Star is a choice game with great story and NPCs and some very satisfying interactions, while Impossible Bottle is extremely well polished and has some of the best puzzles out there.
Cryptozookeeper is probably the least played game on here and if anyone is going to start playing the games to vote better I’d get on this one first. Very squicky/profane and irreverente humor, kind of buggy, tons of interactive NPCs, fully developed pokemon style mini game, music, art, and some very memorable sequences. Junior Arithmancer is just a completely overt puzzle box based on math, which is very very fun.
Dr Ludwig and the Devil and Midnight Swordfight share good writing, a humorously dark vaguely 1700-1800’s ish setting and a vibrant leading NPC. Ludwig has more traditional gameplay en more humor while Swordfight has unique gameplay mechanics and is framed as a play.
City of Secrets isn’t talked about much but it’s one of my favorite Emily Short games. It was commissioned by an Indie band that didn’t use it and has one of the best developed cities in IF, with a thriller story. Wizard Sniffer, on the other hand, is a hilarious fantasy game with tons of NPCs in a large castle using a limited command set.
Birdland was the most popular tribe game for years (maybe still is?) and has great humor with gameplay that contrasts between awkward teen summer camp and dreams where talking birds attempt to recreate human society. Of Their Shadows Deep is a beautiful story of loss and love based on real experiences, with art and poetry.
Zozzled, like Dr Ludwig and the Devil or Lost Pig, is a well-tuned and very funny example of classic parser gameplay polished to perfection. It has a flapper setting and lots of ghost and alcohol themed puzzles. And Then You…is a very detailed and multilevel story involving playing multiple games on a computer and being able to transfer items between games and even real life, while having a thoughtful and touching story.
I’m not sure if the idea is to vote for what you think is objectively best or your personal favorite, but either way this is pretty hard.