can someone help a newbie?

ok, now also looking at an 04 mongoose fairlane and an 03 as well.

any thoughts appreciated

How tall and heavy are you? I ask because the Hoss Deelux is specially designed for taller heavier riders so it's a pretty hardcore bike. Great if that's what you are after. If you don't need it to be stupidly strong maybe look at the Kona Caldera as it would be a better all rounder and it's a very good bike.
Hoss review (not deelux)
Caldera Review

The Raceline looks like it has a few nice bits but nowhere near as good as the Mongoose, can't tell you much more as we don't get them in Britain. Found a review that reckons it's not that hot though - Australian Cyclist

Mongoose have been coming back strong recently and the Duece looks to be very nicely specced and again it's a hardcore bike. Bargain price!

Out of those you mentioned I would say go for the Mongoose Duece as it has superb kit at a good price, if not then a Kona but don't go for the Raceline.

You should find that all the big names make a bike for your budget though so also try looking at Specialized, Trek, Marin, Giant, Scott. If you are looking for opinions about a bike then www.mtdr.com is your friend 🙂 Let us know how you get on!

maybe check the specialized bighits at least some of the cheaper ones www.specialized.com