Many unanswered questions here, so I'll just try to wing it with generalizations.
Since you want to use it to support your plane spotting hobby I'll assume you're looking primarily for a handheld scanner.
I'll also assume that you're not particularly interested in listening to anything else besides aircraft related frequencies.
With those assumptions in mind, the ACT125 seems to fit your needs. Small, portable, and it covers the commercial and military aviation frequencies. It also has frequency search and close call features. Ten banks of 50 channels per bank should allow you to conveniently organize what you want to listen to.
As for the antenna, find one that is made for (or close to) the two air band frequency ranges. The commercial range is just below VHF high band, and the military range is just below the UHF band. Choosing one over the other will slightly degrade reception on one of the bands. I.E., if you choose a UHF antenna, reception won't be as good on the commercial aviation band.
I did a quick search on-line. You can get the ATC125 for $110 through Walmart and ScannerMaster.
Good luck with both hobbies.