Obligatory best food in Ruidoso is in my backyard.
I expect this week to be better given many Texas and NM schools are starting up, but getting in anywhere for dinner has been a nightmare all summer. Best bet is to go early or late. If you don't mind showing up at 5 you should be able to get in places without too much hassle. 5:30-7 might as well stay home.
Breakfast/lunch:. Tina's, cornerstone bakery, Alto cafe, log cabin
Dinner: Rio Grande, Texas Club, Ranchers, Michael J's
Casual: Hidden Tap, Farley's, Anaheim Jacks
Few places that I know take reservations (and will probably turn you away if you don't have them) are Texas Club, Rancher's, Grill Caliente
If you have olds and/or young kids in your party the Flying J can be a good option (western dinner show). Get tickets in advance on their web page.