1. Money (low priority)
2. Lifestyle (medium high priority)
3. Love of work (essential)
I would slightly change point 3 to LIKE of work. Maybe it's just me, but I always found talk of "doing what you love", etc, to engender a sense of pressure in that if you aren't loving what you're doing then you're failing, made the wrong choice, etc. personally, I can't imagine loving anything full time, especially in medicine, whereas just liking a job makes me feel more relaxed :-).
Choosing a speciality will obviously be pretty personal, but I definitely recommend considering all 3 of frugaldoc's considerations. The extra thing I would add, which may be obvious, is the nature of the job itself, which can be difficult to know when you're working as a resident- ie. What does the day to day nature of working as a consulate the look like for that speciality, and are there options within the speciality ( eg diagnostic versus interventional radiology).
Some advice I remember was make sure you don't mind the common stuff in the speciality you're considering. Eg. Don't become an endocrinologist because you once presented a case of Hashimoto's thyroiditis and thought it was really interesting, when you find diabetes management tedious...
There's also a lot of pressure in medicine to devote yourself to your job, often to an unhealthy degree (many of our eminent peers spoken about with respect and reverence also have terrible personal/family lives...)
Don't fall into the trap of doing what others think you should to and consider outside the box options.
I chose psychiatry and am happy with my decision- reasonably interesting job but, most importantly for me, great lifestyle and easy to tweak to your own preferences (at least it is in Australia- public versus private, full time or part time and associated income level).
My plan when I finish in a few months is to initially do locum work only, which is well paid, has a large demand, and provides lots of travel around the country (generally with flights, accommodation, car, etc). I don't have kids so it's easy for me and my partner to do. Also, locum work has the added benefit that you only need to focus on the clinical work (which I like) and not the business/policy/political aspects, which I loathe.
I'm aiming for working about 9-10 months of the year for a few years to finish paying off our house and to get a good start on our investment stash, then will aim to reduce to working about 6 months of the year until FIRE, then just whatever I feel like.
If at any point I get sick of the locum lifestyle then I will probably just go into private practice 4 days a week until FIRE, and just do some occasional locum work for some extra money and exposure to public psychiatry.
Good luck!