Hopefully, I can give you some informed advice because I have done both:
Medicine
Pluses: More rewarding;
more academically stimulating;
more diverse, therefore could consider more interesting.
more choice of career at the end - various clinical specialties, OR non-clinical e.g. pathology, radiology OR pharma industry.
great if you are driven by a challenge.
Minuses: V demanding course
longer + unsociable hours in junior years after qualifying
less money unless you become superb/exceptional and get Harley Street private position 20 years later
you may not like some subjects e.g. I found otorhinolaryngology (ENT) boring, or you may not like waiting hours on end for a baby to be born OR standing in the operating theatre for hours (you have to do ALL specialties as a student).
Optometry
Pluses
Easier course and shorter
Daytime job
Income v low in pre-reg year but then improves to £35-50000 per year after passing PQEs.
Can work flexible days as a locum (earn more and can claim expenses (travel, parking, home office costs) off tax.
Minuses
Routine work might seem monotonous as need to do same procedure on every patient, although it depends how interesting you make it in terms of picking up ocular or systemic pathology (disease), and referring to GP accordingly.
Although income v good, there is not much scope for further progression unless you open your own practice (this is tough these days with multiples like Vision Express advertizing on TV (you could get a franchise with one of them [if you can't beat them. join them!])
IF MONEY IS A PRIMARY OBJECTIVE FOR YOU, DO NOT DO MEDICINE (go into accountancy or business)!
As far as admission is concerned, of course medicine is tougher, but where there's a will, there's a way as I say to my students - check out my reply to your other post.
Good luck!