Glock were the first to popularize and really mass produce polymer framed pistols (though HK were doing it years earlier in the VP70).
10mm is expensive to purchase because it is rather exotic and the recoil is difficult for many less experienced shooters to handle. It was an experimental round designed for the FBI and ultimately abandoned by them due to excessive recoil. Most law enforcement agencies are using 9mm or .40, with a few opting for the high velocity .357Sig.
I see. So if I opted for .40, what Glock should I use?