I just picked up a Harmony Cartridge 2 weeks ago, so I’ve been playing a lot of 2600 lately. For those who don’t know what that is, it’s a cartridge into which you insert an SD card loaded up with ROMs. This allows you to play the entire library on real hardware without having to change cartridges. Freakin’ awesome.
I’m a proponent of emulation in general and I use it all the time (obviously), but for some reason, the Atari 2600 is a platform that I’ve never been able to enjoy much unless it’s the real thing. I want the fuzzy CRT television, the hand-cramping joystick, the guttural noises, the whole shootin’ match.

I agree that MAME has, for the most part, rendered most old home ports of arcade games redundant. There are a few I still enjoy on the 2600 just for their own quirky merits (Frogger, Space Invaders, Track and Field, Bump n Jump, and a few others) but I’ve always preferred the games that originated on the platform. Activision for the win:
Frostbite (#1 hands down)
Enduro
Pressure Cooker
River Raid
Keystone Kapers
Seaquest
Astroblast (a port of Mattel’s own INTV game “Astrosmash”, that I think the 2600 version is far superior due to the support of paddle controls)
Worm War I
Empire Strikes Back
Some others that I didn’t discover until adulthood, but I think are awesome:
Turmoil
Beamrider
Solar Fox (a watered down port, but surprisingly addictive)