OK, here's my 2 cents worth (and we all know that won't buy ANYTHING anymore)...
if the MegaQuilter you're talking about is the "domestic machine on a frame", I'd say "forget it". You will get very frustrated very quickly with the small throat space. However, with that said, if it's the 18x8 (same as a TinLizzie), I'd say "go for it". That's the machine I have, and I love, love, LOVE it!!! Once in awhile, I have a design that really needs a little larger throat space, but I make do. Perhaps one day, I'll be able to get a 26" machine. But for now, I'm happy with mine.
One thought here... I bought mine from SewingMachinesPlus.com - he let me do lay-away - and they usually have some type of special on longarms. As far as needing service - well, I don't know, I've had my machine for nearly 6 years now, and have never needed to call anyone. As I said, I absolutely love it!! Get as much throat space as you can afford... some of the other brands mentioned only have 15" of throat space - and while 3" doesn't seem like much, trust me, you will wish you had spent just that little bit more to get the bigger machine.