There are many, many variables which may affect your deliberations on which way to go, and they may influence different pilots different ways.
Firstly, the relative size of the two airlines. BA is ten times the size of Virgin. It has a long history, the financial markets hold it in high esteem, and it is a proven survivor. Job security at BA is about as good as it gets in aviation. Virgin is a relative newcomer at 20 years of age, and is privately owned. While quite sizeable in its own right, it's not so big that the banks couldn't pull the plug. So it's arguably less secure than BA.
Virgin is longhaul only. There is nothing smaller than the A340-300 in Virgin Atlantic's fleet, and it's unlikely there ever will be. The experiment with Virgin Sun will not be repeated. You have to be absolutely certain that the longhaul lifestyle will suit you, 'cos there ain't no other way! BA offers longhaul, shorthaul and everything in between, and you do get some influence over what kind of lifestyle you want to lead.
There is now not a lot to choose between BA and Virgin on pay (given that Virgin's contracted flying hours are 20% lower than BA's) and, if nothing changes from the post you mention, Virgin's pension is better than the proposed BA one. There are other areas where BA's Ts & Cs are better than Virgin's, but there isn't a lot in it these days.
Retirement at BA is still officially 55. It will change with the new EU legislation, but there are no official statements on that yet as far as I know. Virgin's retirement is nominally 60, with the option to work to 65 in the RHS. That may be significant if you were a late starter on the family front!
So, it may be pie in the sky for you, but it's worth keeping an eye on these issues - your time to make these decisions will come sooner than you think!
Scroggs