The mix I first started playing on was DDR USA because it was the only non-imported cabinet available at the time.
For what it's worth, the first few weeks after I bought the home version for PS1 I pretty much stuck to El Ritmo Tropical, Boom Boom Dollar, and Have You Never Been Mellow, though on the easiest difficulties it doesn't make a lot of difference as to which song you play, just look at the foot ratings. These days I'm sure they have better beginning songs, but those three are pretty much the bread and butter of the majority of first-wave American players. I can't vouch for their musical quality though. >_<
After I managed to reduce the number of times I was tripping over myself (I was
really bad) I took a liking to AM-3p, and that remains my favorite song today just because the first sixteen bars on the hard difficulty are easily memorizable and fun to perform (though it's a pretty easy song by competitive standards).
By the way, if you haven't checked out the website
DDR Freak, it is (or at least
was) the end-all resource for everything DDR. It has step charts for all the arcade versions, tips for navigating the menus on the arcade versions, arcade etiquette and warmup/cooldown advice, and an arcade cabinet and tournament locator by state. (I'm kraniac on the DDR Freak forums, by the way, though I don't post anymore.)