I've started to move on over from AP Lightning to AP Vanguard, and am enjoying myself. Running reinforced frontal/rival/shield with the Halberd as my secondary (VERY convenient for it to go on sale today). I'll eventually migrate over from reinforced frontal to either autorepair/radar/stealth, but I havent decided yet and reinforced front/sides are probably the best you can do with 100 certs.
Pros over the lightning:
Nothing beats you 1v1. Except air, but fuck air

You can 2v1 AP Lightnings, 3v1 any other kind. With an engineer repairing, you can pretty much deal with an endless stream of 1v1 lightning encounters. Great in smaller armor-centric fights.
One-shots ESFs, can easily take out careless Libs.
Losing your vanguard is a bit harder than losing a Lightning. In the Lightning, there will be a lot of deaths that you really couldn't see coming or avoid.
Allows you to play with a buddy.
Ammo is a lot less scarce at lower capacity levels due to the longer reload and higher damage per shell.
Cons:
It moves very slowly. It doesn't sound like a big deal at first, but the improved mobility on even the stock Lightning is actually important in reality.
Dealing with infantry is a nightmare. It's a bigger target, can be chased down a lot more easily, kills them slower, and dies to just as many mines.
If you decide to roll with an armor column in large fights, render range becomes your worst enemy, and unlike in a lightning you can't just run.
Much bigger cert sink than the lightning.