I dont know a great deal about Essex or Brookes but the one thing that will be different is the surroundings. Swansea is the biggest city by some way and is also right next to the sea which the others arent. In terms of rankings the Complete University puts Swansea 32nd Essex 41st and Brookes 48th. For Computer Science Swansea is ranked 23rd Essex 42nd and Brookes 61st. However rankings is not really a sensible reason for choosing a university.
There are many tings you need to consider
Which course do you prefer.
How close or far from home do you want to be.
How do you feel about bigger or smaller cities.
Do you want to be on a campus or based in the city centre.
As I say I know very little about the other 2 but what I can tell is what Swansea has.
It is based by the seaside and the campus is just over 2 miles from the city centre. It is taught on a new campus opened in 2015 and moved into the new Computational Foundry last year. There are very regular buses including a 24 hour service for most of the week.
The city houses top football and rugby matches. The university has a varsity every April against Cardiff University.
The city has a legendary nightclub street known as Wind Street with numerous bars and restaurants.
In terms of restaurants there is a 24 hour Mcdonalds and a Starbucks about 1 mile from the Bay Campus. Swansea has the UKs first Dennys.. You will find restaurants of many different nationalities including Thai, Portugese, Caribbean, South American, Turkish, Greek, Indonesian, Middle Eastern, Japanese, Italian, Chinese and Indian. There are TGI Fridays, Nando, Frankie and Bennys and numerous others.
In terms of shopping there is Wales largest Indoor Market awarded the UKs best indoor market along with an indoor shopping centre and out door shops. You will fine Debenhams, M&S, Next, Primark, Boots, Wilkos, Waterstones and loads more. For food there is a huge Tesco next to the bus station.