Does any one know the difference between the ultra comp engine Vs the hyper 7 engine?

The LX Comp engine is a .26 force and the Hyper is a .21

Which is better?

Depends on what you wanna use it to - racing or bashing - and whether you are a beginner or more experienced. The LX Comp engine is easy to tune and have good low-end.
Which buggy is it to be used in?
And with the Hyper engine do you think pull-start or non-pull-start?

Well Im getting the Hyper 7, its just that I wanted to know the difference. I mainly want to race and bash.

Then you should take the Hyper engine and the best would be to get it without pullstart. It saves a lot of trouble to use a starterbox.
Many tracks will not allow the LX Comp engine since according to the rules only .21 can be used. But if you're competing at club level maybe it can be used. Depends on local rules.