I use the CH340G's - they're cheaper than dirt, so cheap they're not worth counterfeiting, and they come in a SOIC-16 package that's easy to work with, so you can solder on a flying lead to get the DTR pin so you can use the 99-cent-shipped ones to program Arduinii, or make your own board based on them without that much pain. I use a mix of my own-made CH340G adapters (on a custom PCB - I made one that breaks out all the pins) and 99-cent cheapo ones from china. However, apparently making them work on MacOS is tricky :-/