Larger mana potions provide significantly better mana per weight, unless you're throwing the vial away (in which case it becomes a much smaller advantage).
To make hunts last as long as possible, use Soft Boots and (Life Rings or Rings of Healing) as well as potions. Doing this will mean you need to use less potions, meaning you need to take less potions, which (as shown above) are significantly less capacitarily economical (worse mana regain for your cap).
For most players, there will be a need for balance.
Using Soft Boots (if you own them) is almost a given considering that they're best for capacity-per-mana AND excellent money-per-mana (which can only be bettered with Terran Rainbow Shield or Life Rings, and even then only when bought very cheaply from players).
If you're using Great Mana Potions to hunt, you should be using Life Rings at the same time.
Even at the shop price, their money-per-mana cost is comparable to your potions (whether you throw away the vials or keep to sell back), but their capacity-per-mana is far superior. This means that you can either hunt longer with the same number of potions, or for the same amount of time with less potions.
Rings of Healing at the shop rate are too expensive to be justified by most players (since they're far less economical monetarily) and considering their capacity-per-mana is so close, the cheaper Life Ring is probably a better option for most people.