I would definitely recommend rats. They are very intelligent and friendly, much more so than cavies, rabbits etc.
I have owned five, first two I had were Eddy and Bruce and when they died I got another three rufus, otis and colin. They were all different with their own personalities.
There are downsides however. They are prone to chest and resporitry problems usually caused by bad hygene, incorrect bedding, smoking around them and bad breading practices. Also they only have a life span around two years so it can be painful to lose pets so regularly. This is the reason I have given up keeping them.