I bought one Aces pack and one Interceptor, and I already have too many Interceptors as a result, because they only gave you 2x RGPs. The Rebel Aces, meanwhile, handed out 3x Refits and a pair of each title for A-wings and B-wings. If you want to fly mono-builds, you still need to buy two packs... but for a 'one of each', you've got enough.
I sure know which style of Aces pack I prefer.
My pick: An X-wing and either a Y-wing (For thematics) or an E-wing (For balance tweaks, though it'd need to deal with Corran somehow...).
For Imperials, a Defender and a Bomber - in addition to whatever fix they throw in for Defenders, hopefully they'd include a couple more Extra Munitions card+token sets, and another shot at pilots for those two ships would be fun.