I have Vs on my older bike and discs on my newer one and I can't say I notice a huge difference. Having said that, my disc brakes are Avid Juicy 3, which are not the best, with 160mm rotors. I dare say that top of the line 4 pot callipers and big rotors, like on some of the downhill bikes, are significantly more powerful.
The Juicy 3s are the next thing I'd like to change on my newer bike. I don't really need 4 pot, downhill power, but brakes that don't leak from the reservoir cover would be nice.
I was thinking maybe Shimano SLX or XT.
had exactly the same problem... leaking from around reservoir cover. Replaced with Juicy 7s. I wouldn't have chosen Avid again, except they were cheap and I knew they'd go straight on and I could even re-use existing pads.
My theory is that they started leaking because I stored the bike upside down in my loft, so all the fluid ran onto the seals and eventually stripped the paint and corroded the aluminium, then they started leaking.
Total rubbish really because the Shimano (Deore?) ones I had used mineral oil and were better in every single respect than the Avids...
'kin good kit (Charley M)