I have a P95 that I really like. If you just need a dependable gun the P95 is hard to beat. If you want to shoot in competitions buy a glock. Most competitions are set up to give glock an advantage. My competition is living. If someone tries to disarm you the glock's safety on the trigger could create a problem known as glock leg.
The one you like the best. Handguns are like shoes as far as finding one that fits. If there's a range nearby that has rentals, try a few on. It's worth the money in the long run. You'll get as many opinions here as there are brands out there. Fire a few, then decide.
A Sig 210 is not going to fit the $500 budget. There are lots if guns that could though. Police trade in Sigs in the 226, 229 might be able to be purchased near that price. Used Glocks, Berettas, Smith&Wesson, Springfield XDs, may also fit the budget. Rugers should well in the budget. All are very good guns too in that price range.
You're on the right track. I'd say try all trigger types. I love the Glock and Ruger SR series triggers, also check out S&W Sigma and M&P series. I hate standard DAO, can't even understand how anyone could possibly desire them and lack respect for said guns, but I do think you should try them all so you know why one type is better for you.
Give Bersa Thunder 9mm Pro Carry a try. Long da/sa style but great quality. Mid da/sa would be a S&W 3913 or 5906. Perfect da/sa to try is Taurus pt709 slim. All amazing guns!
My preference is sao, and for that there's the sig p938 as the top contender. I find them way overpriced, but quality is undeniable.
I own and have owned several 9mm's from HK's to Sigs and love them all. You may find this hard to believe but my CC is a Bersa Thunder Ultra Carry Pro in 9mm. It is a shooter and has NOT once failed EVER during shooting. I bought the 13 round model with two extra mags (comes with two so I have four total) and my total cost was right at $450.
the one that fits your hand well is the usually the best choice. try out several at the stores or if there is a range that rents them, try out as many as you can. the one that fits you is the one that you will more than likely be the most accurate with.
I would say if you have an indoor range and gun shop in the area? Go there and see if you can rent a few pistols and shoot them. A pistol that feels and fits me well will not necessarily fit your likes and feel. That is the best way to look into the proper selection for "You! Most all of the pistols mentioned here are good pistols. I have several of my own I like. I normally carry a Glock Model 27 for CCW or sometimes my Custom 1911. So good luck on your selection.