Heh, nothing like differences in opinion.
I previously owned the Senn 570 and currently own the SR80s, among several other phones. The Grados are plenty easy to drive. I don't know where the idea comes from that they're hard to drive. Sure, you can squeeze a little more out of them with an amp and I use one with them sometimes, but they sound great out of my measly 5mw per channel MiniDisc recorder. It's not the tiniest bit of strain on MD and the phones sound very clear. The Senn 570 is by comparison more difficult to drive than the Grados.
Someone said in this thread to the effect that they both had accentuated highs and
my ears agree with that. The 570 sound very bright to me, too bright. With the SR80s, I turn the treble 1 step below flat when using my MD and it's just right
for me. But, I read in another thread where someone had compared the cymbal crashes of Grado headphones in general to a car wreck and although that's stretching it a bit, I can see where they might come to a conclusion like that based on what they're looking for in a headphone, so you really need to check them out for yourself. As far as that goes I don't think you can rely on someone else's opinion about Grados. Period. There doesn't seem to be a consensus, just strong opinions both for and against.
That said, here's my opinion.
The Grados are better sounding headphones the Senn 570. In my case, for all types of music. I think the 570s could be good with certain material or tastes in headphones, I just think they're not a good value in terms of what they cost vs. what you get. However, the Senns are WAY more comfortable than the Grados. The Senn 570 are the most comfortable phones I've worn so far, but comfort alone isn't enough.
fredpb and some of the others here have some good advice for you, if you're at all interested in a
closed headphone, check out the Senn 280pro or Sony V6. Both are a good alternative and are less that $100 USD. By the way, none of these are all that comfortable to me for long listening sessions (3 hrs +) but aren't bad for less than that.
If you're willing spend a little more, I think that the Beyer 250-80 would be excellent; good sounding and comfortable, but higher priced and coiled cord (that's a minus for me). If I had it to do over again, I'd probably get the Beyers instead of the Senn 280pro and Grado SR80, and I still might.
What ever happens, best of luck to you finding some great headphones!