Aye, do your research, as always.
And think about your market. If your book is likely to appeal more to a UK audience than a US one you might do well to consider a UK pub -- the sales might be better in that case than going with a US pub. But if it's very US in its appeal, then you'll probably not fare well subbing to the UK. If it might appeal to both, then US ones may well (but not always) have bigger sales but that's something you'll need to research again
It's all about the book really.
Agreed. I'm based in Canada and sold my book to a small press in the UK. The story is about a British historical figure, and while there was some interest in the US and Canada, there was a greater appetite for the novel in Britain. I was thrilled to have an enthusiastic publisher for it.
On the downside -- based on my limited experience to date (I sold the book last November and comes out in two months) -- is that it is good to be aware of some drawbacks if you're looking at a foreign small or indie press. In my case, the publisher has a P-T marketing person/publicist with experience in the UK. When it comes to N. American promotion, I've largely been left to my own devices. Whereas if I wanted to undertake the expense of flying to Britain (which they encourage, naturally), they'd arrange a book tour.
So while the British market is the ideal one, I'm unable (ok, for financial reasons,
unwilling) to take full advantage of it.