Trinity

Trinity is the largest Cambridge college in terms of undergraduate population, and also in terms of college members (though Homerton beats it in terms of numbers of students). It's also by far the richest, and some would say the grandest. Certainly, Trinity offers the real Cambridge experience.
Trinity is also noted for having the dubious honour of being intensely maths-dominated. The list of famous mathematical alumni is astounding, containing such legends as Newton, Ramanujan, De Morgan, Hardy, Littlewood and Babbage. Continuing this tradition, Trinity admits an incredible 50 undergraduate mathmos per year - hardly any other colleges take more than 10! It tends to attract the best of the young mathematicians too, with a large number of the IMO teams heading there.
Trinity's also physically huge. It's situated directly between Caius and John's, its main entrance being the aptly named Great Gate. Walking through the agte, you'll enter the Great Court, the largest courtyard in Europe. You can them basically walk in whatever direction you like, into more large, grand courts. Eventually you'll get to the river and the backs - extensive fields where Trinity Students can bum around in the summer months. You can walk even further, over Queen's Road, to the huge playing fields at Burrel's Field. Then, across the road from the Great Gate, is Whewell's Court, Blue Boar Court, and the Wolfson Building. This is all hidden to passers-by behind a small wooden door, but what awaits you on the other side is amazing. Narnia-like.
Where you'll be accommodated over your years at Trinity is up to you, but in your first year you'll be across the road from the Great Gate. Rents are, due to Trinity's wealth, rather cheap. Also if you do well in your exams, Trinity seems more than happy to lavishly reward you financially.
Hall is cheap, and of variable quality. Formal halls are held five times per week, and are pretty formal (suits, and gowns required). The Bar isn't great really - very bright and little in the way of atmosphere, and not huge for a college this size (It's also not very friendly towards visitors from other colleges!!).
Trinity's boat club, First and Third, is currently dominating the Cam, or at least the men are, with them being heads of the river in both Lent and May Bumps. They also put their name to the college's annual May Ball, arguably the most opulent and traditional ball of May Week.