Up until recently I'd have saved Matt, but I haven't enjoyed the last three performances from Matt (mainly due to Aliona's choreography). For me, Matt's dancing has gone down a few notches, but Gavin has improved tremendously.
I also enjoy the performance of Gavin and Katya as a dance couple, and definitely prefer their choreography. So I'd choose Gavin now over Matt.
In a way, I feel that Gavin embodies what I've always felt Strictly was all about - taking someone with no dance skills whatsover and watching them learn to dance and perform progressively throughout the competition. It's as if the steps, the techniques, the movements and the performance are all now clicking into place for Gavin, which I find (as a dancer) interesting to watch. In contrast, Matt seemed to be almost at the top of his game from the start of this series.