How to pick the right bike, for noobs:
First of importance is style:
Road Bike for distance and speed on paved roads.
Cyclo-cross for gravel roads, some single track off-road trails and groomed gravel trails (can be fitted with road tires for speed on paved roads
Randonneuring for long, slower treks with racks for luggage, great for commuting too.
Hybrid for a mix between a road bike and a mountain bike for crushed gravel trails, paved and dirt roads
Mountain bike for off-road riding, dirt roads – an all-purpose bike (can be fitted with tires for more efficient road riding)
By the way, the notion that a road (or cyclocross) bike is uncomfortable on the back is a myth. Do NOT shy away from picking one up based on that myth, but if you have problems, probably best to consult the Doc. I can say that road biking helped eliminate my chronic back pain.
The idea is to pick the bike that suits your needs best, the two most versatile being the cyclocross and the mountain bike (with a suspension fork that can be locked out). A case could be made for the randonneur or the hybrid but the hybrid, unless it has a front shock, is really not suitable for single track riding, while with a cheap set of road tires, you can make a mountain bike quite road worthy.
My first bike was a mountain bike – exactly for its versatility. I was able to dress it up and do two Olympic triathlons on it and still take it out on the trails with a few simple changes and fifteen minutes.
If money is no object, custom dictates that you buy one of each. In Realville however, making the right choice is a bit more important. If speed is what you’re looking for, there’s only one choice. On the other hand, if you like to play in the dirt, go with a mountain bike. Commuting? Probably a hybrid, maybe a cyclocross bike. Just be careful – I was absolutely certain that a mountain bike was what I needed. Out if the 4,000 miles I’ve ridden so far this year, maybe 200 of them were on the mountain bike.
Next is frame material:
Steel is heavy but an gives an exceptionally comfortable ride. It is also the least expensive of frame materials.
Aluminum (with a carbon fork for road bikes) is relatively inexpensive. though it is less forgiving on bad roads.
Carbon fiber or composite is extremely light and very forgiving. It’s also expensive.
Titanium: if you’re looking at titanium, you’re not a noob and certainly don’t need this post.
Next up is choosing components; shifters, derailleurs, etc. The main rule for components is this: pick the most expensive components that you can reasonably afford. A good group set makes a very big difference in riding enjoyment and durability.
Now, as far as brands go, any of the major brands will make a fantastic ride. The question comes to whether or not you can afford to get out of the big-box bike brands. Going with Specialized, Giant, Trek, Scott, Cannondale – any of the major brands (Fuji, Kestrel, Bianchi, etc.) will provide superior quality, fit and finish. The higher end of the big-box bikes (Diamondback…) are decent as well. As someone who has worked on several of the cheaper big-box brands, my main concern when shopping is staying away from anything with a plastic components like brake handles and shift levers. I personally loath anything with a plastic brake lever, though my wife and I settled for one when we didn’t know any better.
Fit Recovery 
1) thanks for showing the noobs so much love! 2) if I get a hybrid will the “real” riders laugh at me?
Well the easy answer is no, but it’s trickier than that…we won’t laugh at you – we won’t pay you any attention at all. You couldn’t possibly keep up with us for more than a mile (though you’d get points for trying). I may do a post about this very topic because there is a lot of misperception when it comes to the ‘real’ cyclists. Most are not that aloof – they just want to be surrounded by steady people… At those speeds, one little mistake can be fatal, at the very least you’re looking at broken bones and months off. Looked at that way, you’d be a little picky too.