I've been reading about it too. Tim Miller also wanted to triple the budget and go with a more traditional action movie. Reynolds wants to keep the budget low, and maintain the style and feel of the original.I have heard a couple of different things. One was they disagreed on who should be Cable (heard Miller wanted Kyle Chandler and Reynolds didn't). Also that Reynolds wanted it to be more comedic while Miller wanted it to be more serious.
I absolutely have to side with Reynolds here. A hit movie getting a massive budget increase tends to make for a shitty sequel. Keep it low, and depend on story and dialogue, rather than effects.