Best to have a look at your favourite comparison site if you want mainstream cover, Admiral have been competitive past 2-3 years, there's also Aviva, Direct Line who are not on the sites.
If you like the idea of included agreed value, breakdown, modification friendly, club member discounts, agreed mileage discounts, choice of repairers etc. it's worth looking at specialist high performance insurers or classic (depending on mileage), as they might not be cheaper, but they might be better value for you, depends what you want included (or not) really. AIB/Hiscox, ClassicLine, ManningUK, Bridle, etc, spring to mind.