It's all about personal opinion really. Wabara is an England youth international and cost in region of £1-1.5m from his previous club and has been coached by probably some of best staff in today's football and if course Dickov thinks he is better than brown.
He has one edge at moment for me which is true athleticism (pace and power) and that will take him to much higher level.
However if you evaluate rest of his game I personally don't think he is better 'defender'. He is all right foot, brown can play with either. Brown hardly let's any crosses get in from his side and has never been run ragged from a left winger, wabara definately gets caught out more but obviously he has played more matches so will be interesting to see how brown settles in with a run.
I hope they both do well with their future they are sure good enough for league one.