IMHO, the ACE personal trainer certification is somewhat easier to obtain both in terms of content and mechanics (you only have to pass a written multiple-choice test, and there's no practical component), and to maintain after you've been certified (the continuing education credits you need to complete every 2 years can be obtained through a wider variety of providers than NASM). It's also less expensive than NASM. However, also IMHO the NASM training is more comprehensive than ACE's, so you've got a qualitative issue. I think both are equally marketable.
There is a growing demand for personal trainers across all spectra of training issues, for special populations, for elite athletes, for children and teens, for seniors, for the sedentary beginning population, etc. And there is a growing awareness of the value that trainers can add to medical-wellness establishments, as well as health insurance benefits. I'm certified through ACE as a group fitness instructor, and I get literature from both ACE and IDEA (a member organization for fitness professionals from which ACE sprang several years ago), and all of the lit points to the growth of personal training as a maturing career option.
Personal training is still somewhat vaguely defined as a career track; it has no license requirement like a physical therapist (a point of some controversy) so you have to contend with the charlatans as well as the menshes. But it's a good one to pursue here Across The Pond.
HTH - good luck!
a-Jock
