As to systems, here's my play frequency list:
Consoles, in order by frequency used with common games I play:
Atari 7800: Galaga, Joust, Asteroids, Centipede, Ms. Pac Man.
Atari 2600: Star Raiders, Choplifter, Empire Strikes Back, Defender.
Atari Super Pong: Pong, Hockey, Handball, and the other weird game on it that I've forgotten the name of.
Playstation: Spyro and Crash Bandicoot games, occasional Quake II or Doom.
Sega Genesis/32X: Shadow Squadron, B.C. Quest for Tires, Doom, Star Wars
Sega Genesis: Castlevania, 688 Attack Sub, Columns.
Gamecube: Simpsons Road Rage, Gameboy games via adapter: Hamtaro adventure games, Zelda games.
Sega Saturn: Rarely, the usual suspects occasionally, though.
Sega CD: Nothing. I have several games, they all suck.

Old Computers:
Amigas (a 2500 and a 500): Sonix, DCTV apps, The Director, Imagine. An occasional game of Lemmings or Barbarian.
Apple IIe and gs: in CP/M half the time. The other half I'm playing Frogger, Starfleet I, or writing BASIC programs for fun.
CP/M systems: ZSID, RMAC, FTL Modula-2, Turbo Pascal 3.0.
Vic-20 (moving up the list as I write this): BASIC programming, ML hardware hacking, Centipede and Defender.
COSMAC Elf: ML programming, interface projects, teaching classes in electronics.
C-64: Dragonhawk, trying to reconstruct a game I wrote in FORTH but never released due to the distributor losing the license (Groo the Wanderer), Merlin, Wizard, Jumpman.
PC-XT era systems: Assembly language programming for relaxation, usually on an early Toshiba laptop or on a PS/2 Model 25.
Atari 8-bit: Missile Command, BASIC programming.
If I still had a copy of "Run for the Money" for the Mac I'd be using my old compact Macs more. I still have a copy for the 64, but the Mac version's controls were much better--the ones on the 64 version stink.
Many of my programming projects on old micros are attempts to recreate games I wrote "back when" but no longer have a copy of. In the case of the 64 I'm trying to put together a game that was finished but never released (Groo), and all I've found on my workdisks is incomplete copies. On the Ataris I'm trying to recreate Shuttle Defense, and on the CP/M and Commodores I'm trying to recreate a couple of programs I originally wrote for the PET (Quest for the Holy Grail and another that I think ended up being called Castle Rescue or something like that. It was another "Save the Princess" game.) At some point I may finish the version of Holy Grail I started for the 64, which added a real-time combat mode and had a much nicer interface not to mention graphics without ASCII characters. I had about three of seven quests left to write when I broke off working on it, but all the core code was done. Most of what's needed at this point is art.
All this in odd bits of time around my projects with current-day microcontrollers (for which I actually get paid...)
-Mark G.