The first part of this is actually very difficult. The top seven games I've played the most? Have I even played any one of seven different games more than any other besides D&D? I played in a single Champions campaign that I was in for three and a half years almost. Does that count?
I've played a lot of D&D 'cause, unfortunately for me, that's what most people run. I've hardly ever gotten to play the games I love like Star Trek, Star Wars, Traveller, Mekton, Teenagers from Outer Space, Faery's Tale Deluxe, InSpectres, Toon, Paranoia, etc. Some of them I've never played.
As I've said many times before, I don't actually like to play very much. Boy this is hard.
OK, here goes...from most times to least times:
1. D&D ( TSR - Mostly AD&D 1st)
2. Traveller (GDW - Classic)
3. Star Trek (FASA)
4. Champions (Various - Mostly 3E and 4E - A lot of one campaign really)
5. Mekton (R. Talsorian Games - Sort of. We rotated GMs but I was the main one)
That's really it. Everything else were games I played maybe one or two times each. There are dozens of those but none more than any other.
Now games I've run..easy peasy:
I've flown this so often I should get frequent flyer miles on the Starship Enterprise.
2. Champions (4E)
3. Star Wars (West End Games - D6)
4. Traveller (GDW - Classic and MegaTraveller)
5. Mutants & Masterminds (Green Ronin - All Editions including DC Adventures)
6. Dungeons & Dragons (TSR/WotC - Mostly AD&D 1E, 3E, 3.5 and my homebrew version)
7. Mekton ((R. Talsorian Games - 1E through Zeta)
In my 35 years in the hobby (celebrated this past August) I have probably run thousands of sessions of hundreds of different games. Other games I have run A LOT of include Villains & Vigilantes (FGU), Star Frontiers (TSR), DC Heroes (Mayfair Games), Teenagers from Outer Space (R. Talsorian Games) and possibly Shadowrun (FASA - 1E and 2E).
The gaming dynamic I experienced throughout most of my life goes something like this...
Me: I want to play something. Except D&D.
Every GM I met: Cool! We're running D&D.
Me: I want to run something. Except D&D.
Every Player I met: Cool! Can you run any game that isn't D&D 'cause that's all anyone runs?
Lots of people applauding while I facepalm.