Its the one that does what you want in the way you want and within your budget.
If you have plenty of money and dont need it for specialists reasons, then get a mac air or pro according to the spec you need. Its a safe but expensive choice (£900-£1500). Go into John lewis and have a look at laprops so you cna get an idea of what size and weight you need and can cope with, then there are the other factors (besides price).
Power- it has to be accpetably powerful enough or will get on your nerves i3 min I5 better,
battery life, 6hrs min 8h better 10h very good etc as that will lasy you a day between charges.
screen quality- you can only tell from seeing it in rl or relying on a review,
speed- ssd = fast or mechanical drive= slower nit more storage,
memory, will enable you to run several programs at once.
ergonomics etc Keyboard/ touchpad
Build quality
Get a student discount
JL gives an extra years guarantee
Once you select which models you like, then read some reviews to see if they identify things you didnt know about.
Buy it with cc if you can.