How do we measure reasonableness in negotiations like the ones going on between Republicans and Democrats? One way is the party's willingness to compromise. Republicans wanted to defund Obamacare. Democrats wanted a resolution funding everything. Republicans then moved to delaying portions of Obamacare but Democrats didn't move an inch. From this you could conclude Democrats have been more unreasonable.
Alternatively, you could say reasonableness is defined by your position relative to where you realistically will end up. Republicans were never going to get Obamacare defunded. Democrats position was much more reasonable in this regard.
Or you could say reasonableness is measured by the proposed policy's relationship to where we should end up. This measure, of course, makes each person the arbiter of reasonableness based on their political views. Of course, since I think defunding Obamacare is perfectly desirable, I find the Republicans more reasonable.
Or you could measure reasonableness by the likely political reaction to your position. Given that the media is overwhelmingly liberal and, sadly, still powerful, and wants to pin the shutdown on Republicans, Republicans' position could be more unreasonable given where the public is likely to assign blame.
On the other hand, I suspect many of the Tea Party Republicans will do very well with their base after the shutdown. So perhaps both sides are acting reasonably, given their political incentives.