5
REally, for schlepping canon battlesuits, pretty much ANY APC variant is fine, as long as it has the capacity. Some are better thought out than others, or more expensive, or both.
But in general, anything that can keep up with your 'mechs will work. I like VTOL insertion for specific, mission-based games, where speed and unexpected appearance are useful or where an objective can be taken by bypassing the enemy's main battle line, I prefer hovers in swamp or maps with lots of water/ground mix that make walking difficult, wheels for urban (or where C-bill prices actually matter), tracks for everywhere else.
beyond that, 'best' really depends on the rest of your force and doctrine, the mission you're playing out, and the conditions. (you don't take VTOL or Hover in hard vacuum or under water).