DAP will mess up your downloads if you constantly stop/resume/stop, that's for sure. I use mass downloader right now, and it seems to work great. Don't know about gozilla and getright, do they have multiple thread downloads as well?
I'm now using getright. the only other ones I've tried are the ones you listed so I odn't know about net vampire or mass downloader (but since I'm hearing great stuff about them, I'll try them out later). I do like get right but there are a few quirks: it gives me a lot of "server busy, retrying in 50 seconds." to make sure it was b/c of getright, I exited it and d/led via IE and it was d/ling so it has to be getright's fault.
GetRight is da shiz!! The day after I DLed the 110+MB Kingpin demo on a DIAL-UP and GR let me hang up and come back (only one phone line) and restart over a 16 hour period, I whipped out the checkbook and paid the $17.50 the GR cost to register. Two thumbs up.
Getright is the best IMO. I've been using it for 3 years now. It can resume downloads, automatically search for faster servers, limit download speed, schedule downloads for later, dial and disconnect, it does segmented downloading so you can download from up to 3 streams from each server up to 8 segments so your getting full bandwidth downloads, and it has an FTP browser.