My favorites for primary objects are destroy (with defuse option), and carry, so voted for those. They both encourages massive team work from both sides to complete or defend.
Repair,construct and hack is pretty much the same mechanic IMHO, and more fitted for secondary objectives. It’s more lemming type of work, but of course - in some maps they work good for primary too.
Escort can be ok in some cases - if it fits the map layout. One major problem with many escort missions (which I think is very visible in Brink), is the single route problem - it often favors the attacker on the start, and defenders in the end. The MCP worked a bit better, as it could defend itself a bit, and take slightly alternative routes. The forward spawns and transport vehicles also helped to balance it out when the object moved along the route.
One thing I do like about escort mission though, is how they dynamically moves the conflict zone through the map. Implemented properly with a good map layout, it can be great. Maybe this worked best with the tanks and trucks (and boats) in W:ET, when I think of it. Venice map from W:ET is a good example (and goldrush ofc)
:flamethrower: