I don't believe MK1 is online, no.
Still, out of those three I'd go with MK

, you'll probably get the longest play-life out of it since there is so much to unlock. I know DOAU will have a lot of unlockable costumes and stuff, but MK

will have costumes, characters, artwork, videos, etc.
To the poster above who suggested MK

is more "simple" than DOA...I do not agree. DOA is the most basic fighter I've every played. Just because it's got a Japanese staff working on it doesn't mean it's not simple.
When I first bought DOA2 on the Dreamcast, I was busting out crazy looking reversals and moves in no time.
That's not a BAD thing, but I'm just saying that the control scheme and play style of DOA is very simplistic and easy to pick up and play. I'd say MK's style since Deadly Alliance came out is somewhat deeper, especially since each fighter can switch between three totally different styles in mid-match.