Which Melling oil pump should I buy: the 10295, the 10296, or the M295?

All three fit Gen III/IV LS engines; they differ in volume and pressure:

Pump	Volume	Pressure	Best for
M295	Stock	Stock	Stock rebuilds (factory replacement)
10295	Stock	Higher (optional springs)	Stock-clearance engines that want more pressure
10296	High (~18% more; ~8 GPM vs ~6.8)	+10% max (stiffer spring; stock spring included)	Looser bearing clearances, high-mileage junkyard engines, oil coolers

Also: the 10355 is the high-pressure pump for 2005–2017 Gen IV engines with AFM/VVT, which need higher pressure for those systems. The 10294 is low-volume for LSX/Dart blocks with priority main oiling. The 10296 is designed for single-roller timing chains (a double roller may need timing-cover work). High-volume pumps can pull the sump down faster in racing. The stock pump cavitates above about 6,200 rpm.

All Melling LS pumps use the factory pickup screen and include O-rings and interchangeable springs.