purchasing a serger

I am going to purchase a serger soon.  I have about $500 to spend.  I have been looking at the Juki 654 or a janome, or any of the others out there ?  Not really sure... HELP!  Looking for ease of use, variety of stitches, Threading ease, needle type, etc...

I've never used any of the ones you mentioned, I have a babylock serger with a jet-air system. I bought it used & it works great, it's a 4 thread.