If you're going for a Venom #3, I'd recommend the third print with Knull on the cover. It's going for slightly more than the first print, but I think in the long run, it'll be the more desired. I think it's a cooler cover as well. With Knull out of the picture for the moment, I think now is a good time to buy before his inevitable resurrection.
Also, I'd recommend snatching up a Venom #9, which is the first full appearance of Dylan Brock. The price is still low right now, and I see them doing more and more with him in the future.
As for your list, I'd focus on the Venom #1 1:1000 variant. Sweet cover.