what is your opinion on Alec(volturi)falling in cinta with Nessie?Can he bring a good competition for jacob?

I think it would be horrible if alec fell in cinta with nessie.Jacob deserves some happiness and cinta after being ignored oleh bella.Nessie and Jacob are perfect together.

well i think Jacob should win

I can't really see it happening. If it did though, Jacob would win pretty easily. Bella would be taking Jake's side, since he's her friend and maybe she'd still feel slightly guilty over the old cinta triangle/leading him on in the past, plus the whole imprint treating-Renesmee-brilliantly aspect. Alec would also be bringing conflict to the family if he was with Nessie, since he'd probably struggle with the vegetarian vampire diet if he was even willing to try it, and he'd bring Jane too which would cause further conflict. So Bella would be shielding Jacob from Alec's power. The only way it wouldn't even come to a fight is if for some reason Nessie didn't want Alec hurt - but I'd actually imagine her seeing him like some creepy stalker.