I have a 22 year old Cannondale rigid mtb with a 3×9 Shimano Alvio drivetrain that still works almost flawlessly today. The next bike I bought happen to have a SRAM X1 1×11 drivetrain. Its awesome. I don’t think you can go wrong with either, but I’m really in love with the simplicity, capability and performance of my 1×11 SRAM setup. It’s a full suspension 11 speed and it’s not that much slower than my 27 speed hardtail. Granted, it’s got 26″ wheels!