We ended up going to both sides of the falls. Being from the US, you need a visa ($100). We got a bogus story that if we’re escorted by an Argentine for a few hours then it’s all ok. Well, when the border patrol came out, it was apparent that it was not all ok. We definitely sweated it out but were lucky enough not to be pulled over. If you’re from the US, get a visa or take your chances (although I don’t know the consequences if you’re caught).
Brazil is much more tourist-oriented which I don’t like. I am bitter against them because I feel Brazil doesn’t do much to conserve the environment and actually does things to harm it. Case in point, the Brazilian side has about 50 yds of trees wiped out for buses to run. The Argentinian side has this little train running with minimal trees removed (and probably more environmentally friendly in terms of pollution).
Ultimately, it is great to see both sides. It’s a shame to go all that way and only see only side. Make it a point to see both sides of the falls.