Both are excellent amplifiers, you really can't go wrong with a choice. I prefer the VAC to ARC, but it's really personal preference in the sound I like (I've always felt ARC was more tilted to the highs, even their newer models, and I like a full midrange, which I definitely get from the VAC). As far as tube-rolling, while you certainly can do it with the VAC, I haven't had the urge to do so, which is unusual for me.
One thing that Bifwynne points out is a definite consideration with the VAC, as it is very sensitive. I have a Shindo preamp with a lot of gain, and I could barely get the volume control to 7 o'clock before it was at a comfortable volume. I actually have put in attenuators at the amp (something that is built in to VAC's Phi 300.1) to get a little more play in the Shindo volume control. On the other hand, using a TVC passive (Promethius) as my preamp has resulted in no such problems, so you may need to consider the output from your preamp in making your choice.
One thing that Bifwynne points out is a definite consideration with the VAC, as it is very sensitive. I have a Shindo preamp with a lot of gain, and I could barely get the volume control to 7 o'clock before it was at a comfortable volume. I actually have put in attenuators at the amp (something that is built in to VAC's Phi 300.1) to get a little more play in the Shindo volume control. On the other hand, using a TVC passive (Promethius) as my preamp has resulted in no such problems, so you may need to consider the output from your preamp in making your choice.