Russell groups doesnt mean all that much, as long as you feel you will be happy there. But i would go and visit the places to get a feel for them, or even look to see if there is an virtual open day or something on line.Then after a visit/ investigating online, choose 1 as your firm and write it down. Then sleep on it. If you feel the same way the following morning and you feel like its still the right decision, then it is. If you have any doubts, then go for one of the others, and sleep on that too.