Since the upcoming arc of Ultimate Comics Spider-Man is titled Venom Wars, I figured let's make a poll and see who our top picks for Venom is.
If you are not up to date on the Ultimate Comics Spider-Man #18, then SPOILERS will follow.
1. Dr. Marcus
The scientist who previous worked for Roxxon Corp. until his contract was bought out by Norman Osborn. He is indirectly responsible for Miles becoming Spider-Man for not properly storing test subject #42. He's currently working for Roxxon Industries when Betty Brant contacts him in regards to the dead but still intact test subject #42 that hitched a ride with Aaron Davis aka Prowler. He also knows the truth about how Spider-Man(Peter Parker) was created and he has a motive for killing Betty. Plus Venom's line "Trying to profit off of things that don't belong to you. You shouldn't do that" seems to fit with their previous conversation. He could end up being the new Norman Osborn but as Venom instead of Green Goblin.
2. Prowler (Uncle Aaron)
I know he is dead according to Maria Hill. However, we never really found out what was in that box that he stole from Oscorp. He has also killed someone in cold blood so that also fits with the character.
3. Eddie Brock
He was captured and taken to Latveria by the Beetle in his last appearance. He doesn't have any specific connection to Miles but maybe he will come back to take down Spider-Man.
4. Hydra Operative
Hydra is causing quite a problem in the Ultimate Universe. They have been stealing and hacking SHIELD technology. So there is a big chance that Hydra has hacked SHIELD's database and found out Miles' identity.
Some people have suggested that Jefferson could be Venom. So any of other ideas you may have please choose other and explain.