If your mechanical brakes work fine, what are your reasons for upgrading? I'm all for upgrades, but it would be easier to make a recommendation for new brakes if we knew what you're looking for in new brakes.
I have hydraulic brakes (formula rx) on my bike and I love them. Good Hydraulic brakes usually have the advantage of better power and sometimes lighter weight over mechanicals. Also, hydraulic brakes that are bled correctly and used for xc type riding are highly unlikely to fade or pump up, that kind of thing typically only happens on extended steep downhills like you would find while riding DH. As far as brake bias, I may be misunderstanding, but you control your front and rear tires independently, so I'm not sure what exactly you mean by setting brake bias.
If you're considering the mechanical disc route (besides the ones you have), Avid BB7's are popular and fairly cheap. Often good mechanical disc brakes like these will be better than low-end hydraulics.