If I were starting over I would wait on the B-Spec until I got to level 24 A-Spec so I could get the FGT sooner. As for the B-Spec mode I would do it about the same. First driver would be very cool, next one cool but not as much and each driver a little hotter than the one before to pretty much run the full scale from cool to hot as each has thier finer points but early on at low Bspec level the cool driver seems to do the best.
Once you get to level 5 it is quicker to level up your second driver an dyou have more events open for him so it is easy to find one he can dominate. This is true throughout as you get higher levels in B spec and can hire more drivers they are easier to level up.