I switched to petplan because my previous insurers for my last dog didn't cover 'for life' and only covered each illness or condition for a year.My dog unfortunately had a heart condition which required expensive tablets and check-ups for a number of years before she died.So my advice would be read the small print. I'm sure some are cheaper regarding premiums or have smaller excess but you need to be careful what it includes. I'm not sure that the breed of dog makes that much difference,but they probably charge more for pedigrees,and most give a mult-pet discount.
My opinion of petplan is reasonable so far,they have always paid up when I have made claims but I think they are fairly pricey,my excess is £90,and they put the premiums up by about 10% each year,they say because vets put up their prices.