Getting the most out of your squadrons requires some forethought. Probably the first thing to consider is what you want your squadrons to do. Once you know that, it is pretty easy to find the best tool for the job.
When I am building a fleet I usually start with my core ships before I think to much about which squadrons to take. Once I get to that point I start looking at what I want my squadrons to do. Are they there for additional offense, to tie up opposing squadrons, kill opposing squadrons, or do I just need something with all around capabilities? Once I know what I want them to do, I start looking for the most points efficient way of getting that job done.
Between the 2 factions Imperial squadrons tend to be better at anti-squadron work and move faster, while the Rebels tend to have greater hull and anti-ship ability. That doesn't mean either faction is limited, just that they have strengths and weaknesses to consider as you build your fleets.
Additional Offense - This game is about killing capital ships and this is typically my first consideration when I start thinking about what squadrons to include. With no real contest, the B-Wing is the king of anti-ship firepower efficiency. Now, its severely limited mobility is something that you have to overcome, but nothing else gives similar bang for the buck. The TIE Bomber, Scurrg, and Y-Wing also are highly efficient anti-ship platforms, but they are relatively poor up against other squadrons. The TIE Advanced, TIE Fighter, and A-Wing all provide reasonable (although not great) efficiency at attacking ships while remaining very capable anti-fighter platforms. TIE Interceptors, YT-2400s, and most unique squadrons are pretty inefficient when used in this role.
Tying Up Opposing Squadrons - If I am playing squadron-lite then I often simply want to tie up opposing squadrons while my ships do their jobs. So, in this case I am looking for a good value in Hull for the points that I am spending. While Y-Wings and TIE Bombers are really efficient her, the Heavy keyword keeps them from fulfilling this job. For the Rebels, the YT-1300 will be great at this. You can engage ships, which will take a while to kill you, while getting to plink back at them with Counter. For the Imperials, the TIE Advanced also stands out in this role. As a bonus, both of these ships are Escorts. So, you can add in an efficient, but fragile squadron killer with them. TIE Interceptors are a bad choice here although many of the unique squadrons can excel in this role as their defense tokens can keep them around for longer.
Killing Opposing Squadrons - Sometimes, just tying up a squadron isn't enough. Sometimes, it is going to have to die. Squadrons with Intel fall into this category for me. So, when something has got to die right away you are looking at X-Wings, TIE Fighters, and TIE Interceptors as your squadrons of choice. Squads like Aggressors or YT-2400s are also slightly above average in efficiency here, plus have the Rogue keyword, which helps in their hunting duties. Firesprays, Scurrgs, and TIE Bombers are all pretty inefficient in this role. Some of the unique squadrons can boost your anti-squad ability, but you pay a cost in points efficiency overall.
All-Around - For all-around efficiency, the A-wing, Y-Wing, TIE Advanced, and TIE Fighter just can't be beat. I was actually pretty surprised to find the TIE Advanced was so efficient. It isn't great at anything, in fact it is decidedly average. But in this case, that's kinda the point. The Y-wing also comes out as a pretty good all-around ship. It's below average at anti-squad work, but not specifically bad at it. Boosted by some flight controllers and it's actually pretty mean for the points. The kings of the all-around game are the TIE Fighter and A-wing. Even with its Blue die, it can be brought in adequate numbers to threaten any capital ship.