i bought a specialized sirrus hybrid about 2 weeks ago, was concerned about my weight (16 st), this bike edges more towards the road side, but i love it.
i always went for mountain bikes, and from what ive learnt, unless you are going on these kind of terrains all of the time, dont bother:
a) suspension on bikes under £900 are crap, pointless and just add more weight
b) the bikes tend to be heavier anyway
c) all this extra weight on the bike will just slow you down.
depending on what you want the bike for, if like me for leisure rides and a means of losing weight, i would look at the hybrid/urban bikes. i got mine online from evans cycles for £293, they build it all up and once delivered all i had to do was put the pedals and handlebars on, which only took me 10 minutes or so (im not so savvy neither when it comes to bikes

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It sounds like you know what purpose you want the bike for, just thought id mention the hybrid types, as they can serve all terrain types pretty well (unlike mine, some edge more towards the mountain bike side) - this gives you more freedom in my opinion, and you are not restricted to certain areas
