don't get too excited about brand. Many of the brands are actually exactly the same company. I've just had a better quote from Esure, rang them up, told them I was with Sheila's Wheels and they matched the price as they are the same company. The SW branding is very irritating (stupid pink, women in fancy dress, cupcakes) so I rather resent going with them, but the cover is a good deal for me.
NEVER blindly renew as loyalty costs.
haven't claimed so can't comment on that. The scope of the cover is really the important thing. For instance, many offer a courtesy car now but it is smoke and mirrors as you only get it 'if available' and only if your car is repairable. As any car worth under £3k will be an instant write-off in an accident, this benefit is useless.
go through the MSE instructions (it does take ages), answer all questions truthfully, check excesses and what you are actually covered for.
just bought my new insurance today, saved 10% after a lot of comparing and time on the phone.
you'll also need to change your breakdown cover every year, same as your house insurance. Again, loyalty is for suckers.