For me the bigger the better...in my youth the best kits I built were the mpc 1:24 Stuka and P-51 and a 1:12 scale Corvette Stingray with real metal coil springs - amazingly realistic for the 70's.
Actually, my stash these days has: 1:32 for aircraft (even though I have plenty of 1:48 aircraft because of lack of variety in 1:32); 1:350 for ships; 1:35 for armor and 1:24/25 for autos.
The problem I have with most 1:48 aircraft is the lack of engine detail at least with most of the 1:48 kits in my stash. Although, I bought a number of 1:32 Hasegawa Spitfires from ebay expecting to find engines and was very disapointed on delivery.
1:700 ships don't have realistic looking guns IMHO.
I like Tamiya's new trend toward making armor and aircraft in the same scale...I just wish that they had choosen 1:35 for that scale.
I know the larger scales prove to be a hassle in display, but currently I finish so few models that displaying them hasn't been an issue.
Just my take on things!