The five trade-offs
Choosing a room comes down to five things that pull against each other: room type, distance to your department, weekly budget, tenancy length, and what is included in the rent. Improving one usually costs you another, so decide which two you care about most before you start comparing.
Room type sets the floor on price. A studio is fully private and the most expensive. An en-suite room gives you a private bedroom and bathroom in a cluster flat with a shared kitchen, and is usually the best value. A shared apartment shares the bathroom too, and is the cheapest.
Distance is the one students underestimate. A room one transit stop further out can save a noticeable amount per week, but a 40 minute each-way commute costs you roughly 90 minutes a day across a term. Work out what that is worth to you before you take the cheaper room.
Tenancy length is where the real money is. Standard academic contracts run 43 to 51 weeks. If your course finishes in June, a 51 week contract means paying for an empty room over the summer. Some operators offer 44 week semester contracts, and a few offer short stays.