kitty-
personally, i don't think the type of fuse matters, so long as it is sized correctly.
IE: to create a minimal voltage drop situation, fairly large wire should be used. fuses should be sized to protect the WIRING. so ideally, the wire can carry more amps than the solar will ever put out, and the fuse will also be larger than the panels max current, so a fuse "should" never blow.
IE: my 390w array at 24v is connected to my CC with #8 wire. i have it on a 20A fuse. the panels rarely put out over 16amps, so there's a lot of headroom there. i could even use a 30A fuse if i had to as the #8 would still be fine with that.
so fast blow or long blow wouldn't matter, as the current never gets high enough to even tickle the fuse. this is just my take on the situation, others may vary.
personally i use copper bussman fuses. not because i sought them out, but because i salvaged them and fuse holders out of old HVAC units.
adam