The best way to combine these two sentences is Bill and Allen both spent all day Saturday raking leaves to the curb for pickup.
This sentence is the one that best combines the two sentences because it includes a compound subject ("Bill" and "Allen" have been joined by "and") and it avoids unnecessary repetition to refer to the same activity ("spent all day Saturday raking leaves to the curb for pickup"). Moreover, the first option is incorrect because it has been wrongly punctuated: no comma must be added before "too". Furthermore, the second sentence sounds awkward and the last option is also incorrect because no colon should be added after Allen and Bill.
