engifineer

If you are planing on using for any sort of competition, keep that in mind for any sort of motor decision of course. Swapping may rule out some classes in some forms of motorsport where the car would be competitive.

Otherwise it depends on why you bought it like others said. If you love the S2000, then I would put an F20 or F22 in it. If you just care about power and being able to replace parts easily down the road, LS or K24.

Manga_Spawn

So much detail given about the shell..... but really more info about the starting point would be really helpful. What model year is the shell? Does it have everything except a motor or is there other parts missing? How is the body of the car? All there? Damage? Paint? Assuming your post means the only thing missing is the engine then an F series would be the easiest thing as you can just drop in the right motor (by right motor I mean 06+ would need a DBW motor but 00-05 you could do either an F20 or F22 fairly easily). If there is more than the motor missing IE trans, diff, etc etc etc then it starts becoming a more complex thing to make it a running car. You can look at engine swaps but generally you will be looking at a higher cost and labor but this should be obvious. You also have to tell us the intent once the car is complete. Do you plan to keep it and drive it? Flip it? Track car?