None of these colleges has a particular reputation for medicine that I know of, so that shouldn't be a factor.
Christ's is quite good for location. It's got Christ's pieces, a nice green area, just behind it, and is conveniently located next to clubs, shops and restaurants. It's also of just below average size, so you can know everyone in your college fairly easily. The accommodation, especially for 1st years, and the food is not great though.
Trinity is the richest college, which gives it some of the best accommodation and facilities. It's also well located, spanning from the centre of town all the way across the river and to the UL. The only disadvantages I can think of are that it is very large - if you like meeting lots of people this is great, but if you would rather a cosy atmosphere where you know everyone in your year then it might not be for you. I was fairly indifferent about this aspect when I applied, and it turned out to be great - you can still socialise with small groups but just be more picky about who you want to see. Another disadvantage is that it can get quite intense, especially during exam term, because the college has a fierce academic reputation.
Jesus is a nice, friendly college. It's quite large and has big green open spaces. It is a little out of the way in terms of location, though.
There's no real right answer here; go for the one that meets your criteria, and maybe come to visit the colleges or check out http://www.thestudentroom.co.uk/wiki/Cambridge_College_Pros_and_Cons