you can - for the most part - completely ignore the manufacturer claims of 500MB/s speeds. first, those speeds (sequential read/write) are always going to have a 20% or so variance from one unit to another. second, the seq. read/write is not at all representative in how people actually use these SSD drives. and third, a normal hard drive is only 1/3rd that speed.
the real impressive and important numbers are in the 4k read/write performance, where even though the numbers are smaller (and thus less "impressive" to every [male] human being), they are much more relevant and are also 20-50 times faster than what a normal hard drive can do. also, the access time figures - again easily 50-100 times faster than a normal hard drive.
most drives are going to be similar in those important (yet numerically unimpressive) specs, with some being a bit better - but not earthshatteringly so. some drives will have a better warranty, or include nice extras in the package - like free cloning software or a mounting bracket.
for traditional hard drives, look for ones that people say are quiet, fast, and don't take naps. and are cheap. seagate and wd are the main ones. i have a wd green but hate it now - it likes to take lots of naps, meaning playback of clips can have pauses while it wakes up from a nap it shouldn't have in the first place. i like my wd red but it's overpriced. i love my seagate 7200.14 drives - cheap, fast, quiet.