Model scales? O.K. let me try and simplify things a little...
1/72nd The principal scale for aircraft kits and as Robert (Faust) pointed out, is becoming more popular with armor modellers. With reason!! Lots of really nice (and cheap) kits are coming out from companies like Revell...
1/48th The scale 'of preference' for aviation modellers, some armor vehicle kits are available in this scale but sadly very few..
1/32nd Another very popular scale for aircraft modellers. For figure modellers this is known as 54mm. Little or nothing is produced nowadays for armor modellers, in the early days, many armor kits were produced in this scale until the arrival of:
1/35th Scale. The dominant scale in armor kits and (increasingly) in helicopter kits as well.
I completely agree with Faust, Italeri are at the 'cheap and cheerful' end of the market, they are superb value for money, cover subjects which few other companies will attempt and although some of their mouldings are getting a little old, some pleasing models will result with a bit of care and work..
Tamiya is the 'godfather' of the AFV market, they have some excellent kits but do tend to re-release and some of their mouldings belong to an earlier and gentler age

...
Trumpeter one of the young pretenders to Tamiya's crown, this company is really pushing the market to new levels, originality is their keyword...
Dragon the producer 'par-excellence' of German Armor good quality although variable...
Academy another company which is going well. Not quite as 'German-centered' as Dragon, this company is starting to do some nice vehicles for the (minority) allied modeller.....Jim