Perseus, when I started out I wasn't particularly fussy about condition - although always preferring higher grade within reason of cost, it wasn't essential - but as my collection started filling out more I gravitated to higher grades, especially on my favorite titles.

Nowadays, I greatly prefer Fine at least (even for Golden Age comics, although often I have to settle for VG or even VG- there, often because of cost), but Very Fine or better is preferable.

If it's not one of my favorite books, and it's from the 1940s/50s/60s, then VG is often acceptable. But if it is one of my favorite comics - even from the 1960s - generally anything less than Fine is unacceptable, unless it's a tough or well sought-after issue (even then I will, and often have upgraded when I have the chance). Generally, anything from the 1970s on in less than Fine grade I wouldn't even consider, while VF is optimal.

I have a complete run of World's Finest from #46-70, from 1950-55 (and several earlier ones), most of which are VG, but I have several Fine copies, maybe a couple of VFs, and a few GD/VG to VG-; many of these WFCs are formidably tough to find (some are quite scarce), even in very poor condition.