IMHO, the Springfield Armory XD Mod 2 Tactical 9mm is the best out of the box
gun for IDPA SSP.
https://www.springfield-armory.com/products/xd-mod-2-5-tactical-model-9mm/
100% reliable.
Very accurate.
Relatively inexpensive (~ $500)
Magazines are relatively inexpensive (~ $25).
Feels great in the hand.
Nice smooth trigger.
Fiber optic front sight.
Undercut trigger guard (No Glock knuckle).
Ambidextrous mag release that is easy to reach.
Unobtrusive grip safety (for safe holstering).
Other considerations:
Factory 10-round mags are available and cheap. They cannot be converted to
greater than 10 rounds. They use the same base pads as standard capacity (i.e.
10 round) mags, so they are easy to disassemble/clean and third-party basepads can be used (e.g. TangoDown/Vickers).