Hi irky,
'Best' is a very subjective word when used to describe any broker - especially SB firms. Some offer very tight spreads but don't offer any 'golden hello' deals. Others offer you free money to trade with - but may have slightly wider spreads. But this may not matter too much if you're a swing/position trader. Some have great customer service and others - well . . . So, there's something for everyone. It really all depends on your trading style and what you want from a broker.
Your best bet is to write out a list of 'essential' services and 'desirable' services and spend the time visiting all the various firms and draw up a short list. From that, whittle it down to a manageable number - say 3 - and open a demo account with all of them. Once you start using their trading platform, charts and any other services - you'll soon figure out which one you like best. Members will no doubt say who they like and think are best, but keep in mind that their circumstances and requirements may well be very different to yours and, as such, is rather meaningless to you.
Tim.