As with any "what one?" question, you're gonna get ppl simply suggesting the model they have and not likely anything else. Best bet, , go to your local shops and handle the ones that appeal to you. Some will feel better than others. Eliminate them accordingly until there's one or two left to choose between. Then flip a coin. LOL Ok, maybe not but you'd be best off deciding on what chambering you'd want adn then handle some different models to see whcih one feels best to you. Any of the major manufacturers will serve you well and if taken care of last a long time.
Were it me looking for my first auto and had a $600 cap, I'd look at Ruger or CZ for new, maybe a USP from Hk as they're available in that range now being older models. Maybe a FN Hi-Power as well. I'm not scared to buy used either so I'd look at other HK's and some of the better 1911 makes.
If I wasn't too familiar with handguns at all, I'd proberly opt for an easy to shoot/user friendly chambering also. 9mm offers decent shootability, inexpensive ammunition and is quite adequate for personal protection.