i've always had an interest in toying around with recording software. fraps is the basic choice for most people, but i find that it gives me some distracting "screen tear" at some points. it could just be my monitor, but that's one of the main reasons why i'd only use it for replays. someone mentioned bandicam in the thread earlier, and i quite like it. it has options for video encoding settings so your video files won't be infinity gigabytes in size. also, if you use it for different games and have commentary over them, it has an option to record to two separate audio tracks, which is good in case your voice is too quiet or too loud. the one i use most for osu, however, is mirillis action. it's kind of like bandicam, but with a nice gui. it doesn't have as many encoding options, but the newer versions have a built-in thing to stream to twitch (although i think it's a paid service). what attracts me to action is the fact that despite i have a mediocre pc, it's surprisingly stable on most games.
tl;dr -
fraps - pretty good, but it has big file sizes and you might get screen tearing
bandicam - really good
action - good if your pc isn't