Optometry has more opportunities for self-employment. Most are employed in high street / retail opticians, you have to ask yourself is this something you are interested in? Would you find helping large volumes of people with vital routine eye care fulfilling, or would it be monotonous for you?
There seem to be fewer available jobs in cardiac physiology. Presumably, it is harder to get into as one of the PTP streams? What's the career pathway like? Do you need to do the STP to progress in the field?