If you want reliable+strong yet need to stay under 50cc for legal reasons I say go with the honda gx50 or gxh50. I've not had any issues, just routine maintenance on my hs144f 53cc(clone of the gxh50 with a 1.7mm overbore). I haven't had issues with my huasheng engines failing early, my hs142 49cc lasted around 14k miles after I bought it used, and it was from 2009. Idk how many miles was put on before it, but it was thrashed. I did a mountain run a few weeks ago that took me up and down a 2500' climb and back in a lil under 19 miles with no issues with my hs144 with a SBP shift kit and nexus 3 speed hub. I hit between 30-38 mph on the uphill, and 50+ going down. Geared faster I could have hit 60 on the way down but then I would be stuck in first going up.