what works best for me is a clean and dry barrel! cp and j&j are good for what they cost. j&j is pretty quiet as well; tons of porting.
lapco makes good barrels; some of the most polished bores i've seen.
does the stock bolt need to be upgraded? is there anything wrong with it? kind of off-topic, but if the stock bolt works fine, keep it and spend the money on something else, like more paint!