To end this a little, I have two views. First being,
I like Madbull tightbores, I have put a black python in almost every gun I or my friends have purchased, I have seen an increase in performance as a result.
Second,
I have only ever paid for 1 Prometheus barrel, it works nicely, but nothing much higher then the madbulls, however, I was recommended, while taking an AEG disassembly class at APD, that the 6.03 diameter barrel is the best diameter for airsoft, in the instructors experience, and that Prometheus was the best of these.
Hope this helps
I would recommend the madbull, I have never seen any drop in performance over time, if they are well maintained, have had one for in, with good use for over 6 months now.