O.K. you're after votes and opinions, so here are mine. Take them for what they're worth.
V for Vendetta: Excellent concept, but it you've already done it.
Jango Fett: Cool costume, but you've already done it.
Darth Vader: How tall are you? How many times have you seen someone as Vader? Done to death, IMHO. (no disrespect meant to my fellow Vader fans, especiially those at Sith Training Temple.com)
Ghostbuster: Already done it.
Link: Unless someone's played the game, they probably won't get it.
Big Daddy: Ditto.
Arbiter: Ditto.
Anakin: People will get that you're a Force sensitive entity, but may not know if you're a Jedi or a Sith.
Optimus Prime gets my vote.
Optimus Prime would be more recognizable to more people. I have no idea who or what "Big Daddy" is. If you pick a character that is known primarily through a video game, a lot of people are going to be like "*** is that?" or my personal favorite when someone doesn't "get" my costume: "Now who are you supposed to be?" I hate that one.
On you're web-poll you had a section for other ideas. These are a few that you might want to consider. I couldn't add them there so I'm listing a few here. You could also do a Space Marine from the film ALIENS.
You probably know that there is a Predator costume builders website.
http://thehunterslair.com/
As I said before, these are just my opinions.
Regardless of what you choose, choose something
you like and GO FOR IT!