The issue with the L connectors is that they didn't fall off from a jerk, depending the direction. I think Apple may have tweaked the magnet strength a bit, however, as I have not noticed the inadvertent disconnecting as much on my rMBP as I did on the MBA, each with the MagSafe 2 connectors.
I like the new version better. The way I have to charge my Air, it is awkward having an L shape.In terms of durability, I don't think I have a preference.
I think it really depends on where you charge your laptop. For me, it would be a problem to have an L shape, so the T shape that goes straight out is perfect