Somehow it seems easier to answer this broad question when a person has special needs--they are hard to size, or have some physical limitation, or whatever, because then there are limited choices. If you are young, healthy and of average size then you have the paradox of choice.
The big brands, Trek, Giant, Cannondale, Specialized, all have entry level road bikes made of aluminum. Like the Trek Lexa, Specialized Dolce, the Giant Avail and the Cannondale Synapse lines. They are all good, solid bikes. There are smaller brands that make good entry level bikes, often for a bit less money. Like Jamis and Felt. REI has its brands as well. Keep in mind that sizes are not standardized and what fits you in one brand may not fit in another.
I think there are a couple of good things to do when shopping. Find a bike shop that you really like, that will help you find something that will work for you. Given that their isn't going to be a lot of difference between brands I would favor a brand by a shop that I really liked.
That said, there are differences. So, I would try as many bikes as possible to see what works for you. Keep in mind though that short rides are only short rides and you may not be able to tell a lot, especially if you are inexperienced.
If you have a large city nearby that would be great because that would give you a chance to try some of the less standard brands.
As far as used bikes, if you have a good idea on your size you could try those out as well. It can be hard to find what particularly works for you on the used market. I've been watching for small mountain bikes on three different Craigslists for a couple of months and I've found nothing that I even want to call about yet. Keep in mind if you buy used you might need to bring it to a bike shop for a going over/tune up. This adds to the cost.
Last edited by goldfinch; 05-24-2012 at 12:53 PM.
Trek Madone 4.7 WSD
Cannondale Quick4
1969 Schwinn Collegiate, original owner
Terry Classic
Richard Feynman: “The first principle is that you must not fool yourself and you are the easiest person to fool.”