similar to the above comments, it really depends on how's your play style
but, on my opinion, you need both good speed and high main ink for any position
for defensiveness, stick with shooters that doesn't eat that much ink like the zaps and dualies. if you want some range then squelchers are a safe bet
for offensiveness, a personal favorite of mine are the brushes (rollers can work too). you can quickly go to the base with the power clam in less than a minute
if brushes (or rollers) don't work then any weapon that have baller, ink armor, bubble blower, or bomb rush can help surrounding players
one of my favorite things to do is hover around the base, collecting shells, waiting until most of the enemy team left, collecting the last shell, and tossing it at the goal