First you need to determine what type of riding you will be doing. Lots of short hills, heavy loads, you need a geared hub motor. Fast urban riding in flatter terrain, you need a direct drive hub motor. Long grades that go up steeply longer than 12 minutes, only a DD hub motor will do, although they will use more electricity than a geared hub motor in that circumstance.
The 3 hub motor dealers I have heard good things about are ebikes.ca in canada, lunabikes in LA, and Em3ev in HK. luna sells a lot of bafang geared, but they only stocked one to fit fat tire bikes when i was buying. Luna carried replacement gears for those. Last year Luna was selling MAC geared hub that has a good reputation, but only in front wheel configuration.
Several people are selling crystal DD drive, that they brag about.
I bought a 48 v 1200 W geared hub motor from ebikeling in 2017 that was only $221 with full kit. That bike conversion never got me more than 7 miles without failing, but after I got the battery to town and tested it, it turned out the battery was at fault. I've since put 3000 miles on it with only loose motor cover screws as a problem. I don't expect it to last forever considering the price, so when higher tarriffs were announced last summer I bought a MAC12 as replacement. I haven't installed it yet.
As the geared hub was marooned 30 miles out winter 2017-18, I bought a Luna battery and a $189 generic 1000 W DD hub for proof of concept. The DD performed okay, but drug when unpowered like I was in 2 higher sprockets than I really was. So when I got out to my camp in the summer I installed the geared hub. Turns out the controllers were compatible between the two, using a white rectangular connector for the 5 sensor wires. So I'm still using the DD motor controller with throttle. I hated the PAS from the ebikeling controller, and the ebikeling display fogged up in the rain even inside my lawnmower shed.
I'd say anything luna, grin tech or em3ev sells is probably a reliable high end part. I have reservations about sending my debit card # out of the country, if the server is hacked not even the RMCP will care much about a foreigner's problem.
I don't expect to find repair parts for either kind, but I had the DD motor cover off. It uses standard dimension 6801 bearings, so if one of those ****ese bearings wears out, you can get real ones from the auto supply. I've bought them from air conditioner parts catalog, to install in lawnmower quills.