With everything else being equal (ie BTC per MH/s per day), if there is a choice between 5-10% and 1% reject rate, which is the better choice?
Not a difficult answer. Has been answer in this thread and many other threads before it. The MC has ~500 pages of information, a lot of it based around the question you asked.
If high rejects make you feel bad, then move along to another pool that has lower rejects. I personally don't care if I have 99.999999% rejects as long as I am making more than I would at another pool.