I personally can't vouch for either one, but I have always heard good things about both....
AmeriLab Pharm seems to stick out more in my head simply becuase I can't remember hearing a single 'bad' thing about them.... other than their 'mailers' get behind on orders quite a bit, but I guess if you have a good name for yourself, everyone wants the shit, huh? LOL!
Also, I personally wouldn't trust a 'source' 100% if they ALWAYS had EVERYTHING in stock... I mean, shit happens and sometimes shit runs out and I would rather be told that something is out of stock than get something I didn't pay for in its place....
AmeriLab and Syrus BOTH = good IMO.