Just from my short experience, after years of hiatus away from flying sims.
A10C - the only plane that makes sense for a beginner imo, easy & enjoyable to fly, not too overly complicated avionics but with enough depth to keep you interested, has quite a few nice campaigns, only downside is being so old it's not up to date from a graphical pov but in short I love it
F-5E - simple and easy to fly but not too great as a turn fighter, worth it
MiG-21 - I have trouble with takeoff & landings and it's the equivalent of a '70 supercar, again worth it
FC3 - worth it just for the russian jets
I refrained from purchasing Harrier, Mirage and Viggen from the same reasons as you (unfinished, buggy, slow development), I would buy them only when on sale.
I'll get the F/A-18 even if it's gonna launch in an unfinished state because it looks awesome so far.