well you could go with any of them but out of those would say the new os xz-b would be way to go
if get nova the plus 4 team is the best one and one of if not the best motor out right now
werks is good for the price but not on par with nova or os rb r good but no mileage at all
if money is tight you can get the older speed with aluminum head for around 280-300 off ebay brand new and will have a smokin mill all are good just dpends on what you like os speeds r so smooth plus 4 gets good mileage
either of those can not go wrong