warwick has a crap reputation for engineering. brunel is marginally better.
but really it's what you make of the degree. i'm sure the teaching isn't awful, and of course warwick has the benefit of institutional prestige. when it comes to research, i'm pretty sure little goes on in warwick but as far as undergraduate engineering degrees are concerned.. it shouldn't matter too much.
do bear in mind a first from brunel outclasses a 2:1 from warwick.
they're both traditional universities. sure, the consensus is that warwick is more prestigious than brunel. but if you really think about it, it's no Oxbridge. and for that matter, it's certainly no Oxbridge/imperial college in the engineering department.
verdict: go to the university you prefer
source: just finished first year of engineering at a top university. first class honours and have spoken to numerous employers so i know what i'm on about.