I'm a huge fan of the Ruger Standard/Mark series of pistols. I have a Mk I myself. It's just missing the bolt hold-open of the Mk II, and the added "safety" features of the Mk III (mag disconnect, loaded chamber indicator). The whole series is very customizable, comes in a variety of shapes, barrel lengths and weights (they have a polymer framed version shaped like a 1911's frame and then they have tapered barrels, heavy barrels, fluted barrels, and slab sided barrels), and is as reliable as your ammo will allow.
They've been in continuous production since 1950 so accessories are plentiful, as is troubleshooting info and spare parts.
and yes, IMO a pellet gun would be too far away from a real firearm. There's no rifling so you won't get a good handle on your accuracy.