The older arcade games kick your ass because they needed quarters, and lots of them. I wouldn't even try to fight against the AI in any version of MK3, be it UMK3 or MKT.
MK9 is THE game to play if you're new to MK. Has basically every character from the original trilogy sans Cyber Smoke, and the best characters from after MK1-3. Thankfully, the console versions have a Komplete Edition that has all the DLC unlocked, because unless you already bought the game, you can't buy it on digital storefronts now thanks to one of the DLC characters being Freddy Krueger, and I assume that once the license/agreement's duration expired, Netherrealm and Warner Bros. had no choice but to pull the game from said storefronts, Steam included. If you want...