I hope these are the AM3+ boards?
Well, looking at the back panel of the 870 board you get 4x USB 2.0, 2x eSATA and 2x firewire ports, plus your 2x USB , 2x USB 3 and sound outputs.
On the 880, its graphics, 4x USB 1, 2x USB 3 and 1x firewire.
If you have a graphics card already then I say go for the 870. You cant have too many USB ports