I have accounts with CMC (Deal4Free) and Capital Spreads.
Capital Spreads have a more user friendly interface and very good Customer Service. If there spreads match CMC on the product I intend to trade., I trade with them. More trades are rejected here "Price Expired" They only reject when the market moves in your favour not against !
Remember that when you trade with a spread bet company (a bookie) you are trading against their price not the market. Prices are CLEARLY biased. I think there is good reason to believe that these companies alter the bias, after you have entered the trade, depending on if you are long or short. In otherwords they offer different spreads to clients depending on which direction they are trading long or short. Heavily denied or course.
The advantage of spread betitng is that you can enter the market with a few quid, good when you are getting started. However, once you are at 10.00 a point sort of level, no reason not to switch to direct access, other than the tax issue of course.