Lifestyle wise I do think Virgin has more to offer. Yes, the perception is that you will be away from home a lot more, but as someone already mentioned, in reality this may not be the case.
I have done exactly that what you are contemplating, I have left Monarch for Virgin. I too find that I actually have more time at home now than in the charter days. It's something many people only flying short haul find hard to believe, but it's true (what's more, I am better rested so I do enjoy those days off a lot more). With Monarch I was away a lot, either on long haul at some other UK base. Then when you did have some days off, this block of days was often broken up by a nice standby in the middle. Not conductive to a stable lifestyle.
As I said, I also did the occaisional long haul with Monarch, something I did enjoy a lot and which gave me confidence that I would be able to deal with the Virgin lifestyle of permanent long haul. What I had not foreseen though, was the immense effect the bunk has on you well being. Just being able to lie down a couple of hours on a long flight - even if you don't sleep - makes such a difference in how you feel when you arrive, and even more importantly, in how quickly you get back into the rhythm of things.
All of this is not a knock on Monarch as a company. I think it is a very well run company and I have had a great time there. Things are moving along there pretty quickly at the moment regarding time to command, so you could do a lot worse than to stick around. Ultimately, and I am sure I am telling you noting new here, it is a lifestyle choice. Long term, what would suit you better?