This can either be for PS3 or PS2, but I'm wanting to get an MK game. Ideally I'd like to get the original Genesis game but my Genesis died a few years ago despite being taken care of very well and I'm not about to try and find a new one. So the consoles I have now are PS2 and PS3. So which MK game on either platform is the "best" one to get?

UMK3

Just download MK2 on ps3 and get MK vs DC for ps3 too. MK2 is the best 2D MK game and MK vs DC is the best 3D one. 

UMK3 is best-known for being the most balanced. I prefer MKII, personally, though.

I still think MK2 is the best. Download it over the Playstation Network if you can.

Yep your probably best off with the 2d ones.
However I always liked Deadly Alliance on the ngc/ps2/xbox1 too, the other 3d's not so much.

I'd say Mortal Kombat Trilogy-it's got the most character, and, although it has the ridiculous boss characters, it also has 25 or so characters who aren't.