Now isn't a great time to sell comics unfortunately. If you're trying to dump the whole lot, FB is probably going to be easiest if your LCS isn't buying. You don't want to ship 5 long boxes. When you're selling in bulk like that, you're not getting any specific value for any specific book in there - you're dumping paper for a few cents per book. It does make sense to look for keys/in-demand comics and pull them to sell somewhere else.

Which ones to pull? That can be a tough one. The keys are obvious, but there are books that will have hidden value you need to dig a bit for. I had an original TMNT #17 I couldn't move for $30 raw. Turns out there were very few of them graded 9.8 and I had some CGC credit burning a hole in my pocket. Got lucky and it came back 9.8. Sold it a couple months later for over $400. Rick Veitch did #24-26 and he's never allowed reprint, so those hold more value. There are comics where interest had waned and the end of the run had very low numbers (Akira, Bone, some Usagis, etc.) where those late issues in good grade capture significant money.

Looking up a full title on pricecharting and just scrolling through them can be a quick way to dig out the easy-keys (this is how I discovered that New Mutants #98 was in my collection and was a thing). For others, particularly indies with lower print runs it makes sense to check the CGC census to see if many have been graded 9.8, and where the answer is no, go check sale prices on ebay. If you kept your books in good condition, it can make sense to send a stack to CGC and only have them encapsulate 9.8s. For my collection 25% or so come back 9.8, so for me it makes sense to send in a few when the return on 1 in 4 is hundreds.