1) Define "big"
2) Are you limiting yourself to pythons, or are boas in the mix too?
You're limited in your options if you're looking at 'true giants' such as burms, retics, afrocks, green 'condas.. because there are so few species that attain that kind of size.
Are you looking only at things that have the potential to break 150lbs? To any BP owner, a 30lb snake can sure seem huge.
Pick any species that reaches sizes over 30lbs, and I'm sure you can find individuals that are incredibly calm as well as individuals that come out swinging when you open their enclosure. There are no set rules for species personality, heck there was a thread started today asking about what to do regarding a ball python that was very defensive.