Also
Coricus
I see you there.
If anyone can gush on 3D Sonic it's you; lay it on us.
Well typically when the topic comes up I duck out because people don't know how to behave, but if I'm being rung up,
I haven't played every 3D title (SA2 being the biggest absence of note as far as games with decent amounts of people noting them as favorites go), but I'd say my favorite is probably Adventure just for Sonic's route alone. There's just something so intensely satisfying about the gameplay involved, and it's pretty much the longest route in the game as well. I'm saying this as someone who played this after Generations came out, this isn't nostalgia talking it's just good. The other character routes run on a bit of a sliding scale, but Sonic's is both the most replayable and the biggest. Chao garden isn't half bad as a distraction, either.
As far as Modern style specifically goes I'd say Generations is my favorite, but I think there's also something to be said about the various DIMPS titles that cropped up on Nintendo handhelds for a while as they're essentially the evolutionary predecessor to Modern style and in my personal opinion a more pure incarnation of it. I don't particularly like Sonic 4 (although I wouldn't say it's terrible either, just not particularly enjoyable compared to most Sonic games), but I feel like the handheld "ports" of Sonic Colors and Sonic Generations get unfairly maligned for being different games than their console counterparts, and this is at least speaking as someone who owned both "versions" of Generations. In that specific case they both follow the exact same plot, but they're really more companion games than anything. Almost entirely different level selections.
I'd say Sonic 2, Sonic Adventure, Sonic Unleashed, and Sonic Generations is a good Sonic loadout for me, and I tend to like each one mostly for different reasons but with a tangible sensation of speed being a common unifying core.