Hi
I have used Delta Index and IG Index but didnt have the problems you talked about(touch wood). But I have read complaints about every SB company out there on other websites so I think people have had problems. Maybe it can be down to the software they use(many seem to use the same software) or it could be the company, I don;t know. What seems to be consistant though is that when something does go wrong, they will not give money back, its kind of tough luck.
Re the FTSE, the Daily FTSE on Delta has a smaller spread and lower margin if you just want to hold for the day.