Oddly enough, I only have 2 fullsized headphones in my house, and they are these two. Both of them are good headphones.
I prefer the Grado's personally, but the Sony v6 is good too. The sony v6 is a tank, but the simplicity of the grado makes it fairly durable as well.
First off: if sound leaking out/in is absolutely impossible (going to be using them in a loud environment, or a really quiet place likea library and you don't want to bother people) don't go with the grado, or any other open headphones, as they let sound leak out.
Secondly: What music do you listen to? The grado's are great for rock and roll, jazz, folk, female vocals and even classical solos/chamber music (not full orchestra), but I wouldn''t suggest them for hiphop, or bass heavy techno, although they can be made to work well with it if you are willing to 1: do some eq-ing and 2: some basic mods.
The V6 has the edge over the Grado in terms of clarity, they literally reveal everything about the music, but they don't seem especially "musical" compaired to the Grado, which adds a coloration to the music that I find very desireable. Keep in mind that compaired to consumer headphones/earbuds, both of these will show you things in your music that you never knew were there. Both the Grado and the v6 have a fair amount of treble and not a lot of bass in stock form, so if you want bass monsters, hopefully someone else will be willing to offer some advice in that catagory, although I have heard good things about the dennon d1001, and some others, i don't have any experience with them.
Honestly, I don't particularly enjoy the v6 as a pleasure listening phone (it's great as a monitoring phone though), perhaps someone else with experience with other headphones in the pricerange could drop by and make a few other suggestions. if isolation isn't a problem though (it might be on a bus, but probably not at home) and you listen to a lot of rock/metal/or female vocal music, i'd suggest the grados. If it is a problem, or you prefer more Dubstep and hiphop, I'd bet that there's a 3rd contender out there as an option