AR-15 = good for killing mice, ugly, plastic.Mini 14 = proprietary parts that when...not if....they break has to be sent back to Ruger who may or may not have the parts for older series rifles I had two extractor break and one firing pin. Mini was gone for months.
M1 carbine = can still get parts, but they are getting expensive, ammo and magazines are hard to find right now. Ammo expensive
AR-15 = ammo still available and fairly reasonable, parts can be found almost everywhere at reasonable prices.