It really depends on how important E+ is to you and when you book flights. If you are tall (like me), no amount of good service can make up for the fact that VX has hard plastic seat back pockets that make its coach unbearably painful. What can make up for it is the generally available MCS, but you have to be willing to pay for that.
If you generally buy tickets at the last minute then you should consider a different airline that provides immediate upgrades to F for elites on full-fare tickets. CO does that (but switching now doesn't make sense given the merger) - and I suspect there are others.
Of course, since you say you regularly have trouble making 2P on United, VX is probably a better choice anyway. Few airlines are good at taking care of people who are not elite, regardless of how much they actually spend on flights. VX is a nice exception to that rule.