S&W M&P15 SportII is probably a great buy for most people at $500. Just maintain it properly, keep it lubed, and you should be good to go.

If buying a Palmetto State rifle, I'd buy the upper and lower separately in order to save some money. I'd personally stick to their fixed front sight configurations. The Palmetto "Freedom Rifle" was the first AR pattern rifle to pass AK Operators union 5000 round torture test, for whatever that's worth. The rifle was pretty over-gassed, but very reliable. LOL Rob Ski makes some great videos.

Another option is to buy a complete lower from Palmetto equipped with Magpul MOE furniture for about $150. Then find a decent upper like BCM's Standard 16" Mid Length (LIGHT WEIGHT) Upper Receiver Group (.625FSB) with BCM Bolt Carrier Group and PKMR handguard for $635. This would be a pretty nice setup for around $785.

If Palmetto still sold the nitrided pencil barrel uppers, I'd buy one tomorrow.