Welcome to the forum.
There is no easy answer to your question. Unfortunately it will most likely come down to your own trial and error. You can try taking a look at the spread betting companies comparison table
and maybe read some of the reviews on there to help you.
Personally I like trading with SpreadCo, Capital Spreads and IG Index. Why three companies? well some offer instruments that others don't and some have tighter spreads. I find it's always good to keep your options open when having spread betting accounts.
That said, I think FinSpreads still offer £0.1 per point trading for the first eight weeks(don't quote me on that, it may have changed, or I may have gotten it wrong). Trading with a small stake can be a great way to get started. Also some of the companies offer demo accounts which is a great way to try before you buy, so to speak. My comparison table, link above, will tell you which offer demo accounts etc. Your best bet is to take a look on there.
May the markets be with you!
The Spread betting beginner