Sram is getting a lot of respect on the 'cross circuit, but the one thing that everyone is deviating from in the Sram line is the OG1090 cassette, the OG1070 will handle mud and other debris a lot better because it is a multiple piece cassette, whereas the 1090 doesn't have deep "valleys" between the "cogs".

Good luck!

::EDIT:: It might be just me, but with numb fingers downshifting on Shimano shifters can be a little clumsy, so there is a welcome advantage to Sram in that sector.