Non-US Amazon Affiliate Websites?

Hi everyone,

I'm UK based and considering launching an Amazon affiliate website.

My experience with this is creating a US website a year or two ago, with moderate success (it was a small niche, but did relatively well, considering.)

I'm considering investing in a larger, more ambitious website. However, I'm not sure whether to target a US audience or create a website specifically for the UK. Obviously the US website would have more potential but would be significantly harder to rank. Vice versa for the UK site.

So basically, my question is this: US website or UK?

I have some ideas but have yet to thoroughly analyze niches. I can probably rule out the super-competitive US niches, but would targeting amazon.co.uk open the door to them? I have no idea how competitive UK SEO is versus US SEO. Any idea?

And for anyone who has experimented with a non-US website, how much did this restrict your earnings? But did it make it easier to turn a profit?

Thanks in advance everyone!