Welcome to X-WIng!
Aside from the epic ships and core sets, there are actually only 4 multi-ship sets out at the moment (and one on the way) and it seems like you are already somewhat familiar with them.
Rebel Aces In terms of ship "variety" this is pretty good. You get a B-Wing which is slow and "jousty", and an A-Wing which fast and "arc-dodgy", both are popular ships from the movies that people will recognise, and both exemplify a different aspect of the game. Unfortunately, the upgrade cards included in the box won't allow you to build much on their own.
Imperial Aces This is actually just two of the same ship (Tie Interceptor), so not great variety, and it doesn't include the best Interceptor pilot (Soontir Fel), who comes in the single Interceptor expansion pack. However, Interceptors are awesome fun, one of the best arc-dodgers, and this set comes with some pretty great upgrades.
Imperial Veterans This one has two different ships, so points for variety. One of those ships is a Tie Bomber, which isn't very inspiring, but I guess it is at least unique. It includes reasonably good upgrades to get started with the ships in the box.
Heroes of the Resistance This one isn't released yet, but it's probably a good way to get the Millennium Falcon, and you'll get some additional Pilots for all your t70 X-Wings.
Most Wanted This is kind of the core set for the Scum and Villainy Faction. You get three models (2x z95s, 1x Y-WIng) which can be used in Scum or Rebel lists (if you have the rebel cards), and you get dials and pilot cards for the Firespray and HWK-290 to use with scum (if you have the ships). It wouldn't exactly be "cheap" to get all the ships and cards to round it out, but it's reasonably good value since it does a lot of double duty. The z95 is a cheap "quantity over quality" type ship (reasonably competitive), the Y-Wing is a standard turret platform, the Firespray is a large ship with a lot of ordinance options, it's probably the most fun way to explore things like Bombs (especially the scum pilots), and the HWK-290 is a support ship, but can also double as a turret platform. The upgrades in Most Wanted probably aren't especially useful for someone getting started.
To be honest, you'll probably find it difficult to collect a good repository of upgrades without "lots of purchases", so it might be better to proxy them if you are just playing casually. Sites such as
http://xwing-builder.co.uk/ are good for seeing what's available.
The usual advice is just to choose ships that you like. Most of them are perfectly usable and balanced for casual play.