Which sugar to use depends really on what it's for, but light DME (dried malt extract) is generally the best one to use. It is more expensive but you get what you pay for. It actually enriches the flavour and head retention to a certain extent and never makes it taste cidery. You do also need to add 25-50% more than you would with corn sugar/dextrose etc. Brewer's sugar is just a mixture of dextrose and DME, I think 50/50. There is quite a lot of info about all this online,
http://www.howtobrew.com is a good place to start and it says quite a bit about different sugars.
Good Brewing
PoP