I'd go with Kurt at the moment.. Doumit is yet to get his timing back and won't be healthy for another week or two.
Kurt on the other hand has always been said to be good and is finally showing it. When your looking at a catcher, you always want average. SBs/HRs are at a premium in this position. You'll rarely get a good HR hitter from free agency at catcher. Kurt has average and that's good. I look at it like this, he hits for average and whatever else he gets is just a bonus.
Ryan Doumit has been injured this year and is more injury prone then Kurt Suzuki. I'd take Suzuki as he hits for a solid AVG. and has good RBI numbers for a C, especially one playing for the Athletics. He is also a guy who can steal you a base now and then as he will most likely end the year with 10 SB. GL