Worth checking out each one's strategic priorities to see which might be more interested in your kind of work. Wellcome are an odd one, IMO, in terms of what they're interested in. For example, clinicians can apply for public health type project funding, but if you're a non clinician it's assumed you want to do basic science. And then they're *really* into genome wide association studies.
Does your department/faculty do any specialist workshops on applying for fellowships and so forth. I get the impression there is often unspoken stuff that senior academics know about regarding funding chances, that they might be able to share with you.
I'm sure some are easier to deal with than others but I think ultimately it comes down to what career stage you're at and what your proposal is about.