I chose "Republicans gain in House, Senate relatively unchanged" because that is closest to what I think will happen, but not quite.
I believe that the GOP will make gains in both House and Senate. Dems will still control both houses, but Republicans will be able to effectively filibuster ALL Democratic proposals, and I believe that this is what they will do. My prediction is that the GOP will pretty much shut down the legislative process, except on a very few bills. I also predict that, as a result, Democrats will at least give serious consideration as to changing the number of what constitutes a filibuster, which, IMHO, is a dangerous move.