According to CubeCobra, the most popular ones, in order, are:
To me, these are the big three in a lot of ways. I previously ran all three, and currently don't run any of them, just for space reasons.
Booster Tutor is inconvenient relative to the power (though the fun is still there) and is probably not going to be stuck in the on-deck binder forever. The novelty of rolling a D20 for Sword of D&D is kind of lost these days. Blast from the Past is excellent still, but a bit complex for our typical player -- that said, in moments of weakness I will certainly add it back in.
The next slate by popularity:
Again, no surprises here. Only ran
Crow Storm of the bunch myself in the past of these three, but I've got an
Earl of Squirrel sitting anxiously in my on-deck binder as well, and both are certainly of a high enough power level and interesting in terms of gameplay.
While I'm not sure why folks would run
Super-Duper Death Ray post-Ikroia except for the name is funny, but Usman has been a big proponent of
GO TO JAIL for years now and has almost convinced me. I currently run Urza, and happily so -- at 720 cards, I don't feel bad having a miser 5-color card, and since Urza's printing, I've been delighted to run him, and have won (and lost!) many games off of the RNG that doesn't feel oppressive or unfair (especially with the mana cost and low loyalty) but is exhilarating and powerful all the same.
Other Silver-bordered cards either myself or one of my friends have run and had good experiences with:
I was incredibly sad to cut
Very Cryptic Command but the triple blue pips are something I can really only justify once in my cube.
I've also always wanted to play
Hangman but he's just way too wordy to justify.