Just as a basic principle, it's always sensible to stick to ingredients from the original country for a style, to avoid any weirdness that comes from another country trying to "interpret" an ingredient. Particularly in a case like this where malt character is an important part of styles like bitter.
So as long as you have reasonably easy access to British malts, you can't really go wrong with one of the old favourites like Otter or Promise. They're old favourites because they just work. Beyond that, strangers can't really help, it's up to you to work out what you like (including which maltster you prefer).
OTOH, you said "popular" - and it's worth noting per
my chart in #2368, that despite their prominence in our world, Otter is barely a rounding error in UK barley production and Promise isn't even as much as that. The varieties that are "popular" in UK beer as a whole are the modern ones like Laureate and Planet, which have higher yields that drive down the cost of goods for big commercial brewers like Greene King and Asahi-Chiswick. They're the varieties that go into generic UK pale malts.