Plenty of choices which come down to your personal preference... like for example Classic, Bug, Blob, Hawk or Shark eye...
You indicated Classic (Love Classic - I used to drive a STI v3

)... so 2 door or 4 door? STI, RA, R type, P1... choices choices.
Check out insurance though - it can really catch people out. Impreza's are hard to get insured and typically expensive if you do get insurance. There's definitely a difference between an imported vehicle and domestic car for insurance -- but then also the specs differ and depending on your preference certain models can only be got as JDM (Japanese Domestic Market) and hence imported.
AA car insurance is good as is AXA.
www.quoteme.ie is good for comparing some, though did find that going directly to the insurance companies after gets you a better price.
Be careful with any car with obvious modifications (like Front Mount Intercooler). Whereas there is great value to be had with a car that's already modified it can be very difficult to get a car insured if modified (not always, but some companies point blank refuse modified Impreza's).
As per Scoobysub... if you see and like a vehicle always worth checking with the folks here as often they might know more history.
It's worth holding out for a good one (getting more scarce now)... as a bad one will cost you as much in the end to put right.
Good luck with the search... once you go

you'll never go back (and when you do... like I did... you'll be back

)