Bizible is probably the most widely used (based on the instances I have peered into (we're consultants so we see a lot of Marketo instances and stacks). I'd probably evaluate Brightfunnel as well but don't take that as a recommendation as much as, I know that people use them but not to what effect.
What do you need to do? You need to understand the resulting report and decide how it might work and quiz vendors on how they handle attribution fully.
Bizible, I agree is likely your best bet. FullCircle is ok from what I've gathered. There are some newer vendors as well.
Brightfunnel just got bought.
You mentioned other new vendors other than Bizible, Full Circle and Brightfunnel. What are those?
Also between Brightfunnel and Bizible, which one would you recommend