Sometimes I launch my rocket perpendicularly to KSC and I keep it that way through the atmosphere, so I end up having a very high apoapsis and a very eccentric trajectory, so I can't wait until I reach the apoapsis to start doing a burn. Now I'm wondering: what is the best (most fuel efficient) way to achieve an orbit in this case? Should I do a burn along the prograde vector (chasing it) or should I line up the rocket with Kerbin's equator (keeping it that way) and then do a burn to achieve orbit?