I'll say it - best combo of overall great suspension and greater reliability is more likely - a summit or maybe the yet to be proven yamacat, and that may be a big yet. If those are your key buying points. A nytro needs so much suspension reengineering it can't be considered. I wouldn't call a M more reliable, stronger motor, but many other niggles, they are getting better, maybe the viper experience will help them around the corner. The yammacat mt viper will be the real proof.
With that said, a new stock RMK that is well maintained, always warmed up before you crush the flipper, well summerized, good fuel, along with the other recommendations, can be very, very good reliability-wise, on average. Stock suspension has good points and bad points. All four OEMs have decent sleds right now, but what works best for you? I try them all, also have summits, so brand is not critical. Love the RMK chassis for me, so far.