This is extra important with the Glock 21, because it has a large grip that turns alot of people away from it. They make the 21SF model, which has a slimmer grip (front to back). I think the 21 would be your best choice if you are not going to carry concealed.
I like the 30 a little more than the 36 because I can't get over the magazine capacity of the 36...if I only wanted a couple of bullets I could carry a Smith 442 or a Kahr PM40, and having something more concealable. That being said any of the three .45ACP Glocks are very good pistols.
I would also encourage you to check out the Springfield XD & the Smith M&P. Both are very good polymer, striker-fired guns like the Glocks and are in the same price range. The grips are slimmer, and you may find them more comfortable in your hand if you don't like the feel of the Glock 21.
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