Also at the sort of price point you're interested in (very similar area that I've recently been looking at) there are always going to be caveats so it comes down to what surfaces you're going to be riding on and what you're generally wanting the bike for....e.g commute, general riding, training.

You'll find that as soon as you go near a bike with front suspension, that will have an effect on the groupset/chainset because some of the cost is used on the front end, a bike with rigid forks will not only be lighter but may have slightly better spec elsewhere - similarly hydraulic brakes may affect the spec of other components compared to an equivalent model with v-brakes or mechanical disc . A good groupset for the price may mean you end up with a frame that's not quite so good or comes in quite heavy. I think like others have said that you really need to weigh up quite a lot of areas and find a bike that suits what you need. I'm sure there are loads of 'generally good' bikes but there may be a hidden gem that caters better for your needs if you can elaborate more.

You may also take into consideration how long you're likely to keep the bike for and whether you'd upgrade parts over a period of time...if that was the case you may be tempted to go for a bike with a better frame and brakes because items such as shifters/front and rear mechs are relatively cheap upgrades and aren't maybe that important at the time of purchase - that may also answer your shimano/SRAM question.

With regards to Shimano/SRAM....you get what you pay for. I wouldn't say that one is 'better' than the other but people do have their preferences whether that be slick shifting, quiet and precise (shimano) or often that little bit noisier but superfast (SRAM). Some people get to the point whereby they swear by a particular brand but most people can appreciate both serve their purpose either way. You can google the tiers of shimano/SRAM to find out which particular range is competing with each other but again at the price bracket you're looking at you're likely to see the same groupsets over and over again, just beware that if you see a bike with what seems to be a better groupset than another bike, it's possibly lacking in another area such as cheap brakes/finishing kit or forks. Now is a good time to look at bikes in the sales as we're only a few months away from new models being advertised and the 2014 and 2015 ranges often get big discounts.