Druid/Sorcerer:
Druid and sorcerer summon are the best one for blocking some bosses like mini Falcon Bosses and are a pretty useful tool to avoid traps, for example when sometime you get trapped by 8 monsters you can summon your creature and attack some creature , this summon will do an "exeta res" and you can scape from the trap, that trick save me many times.
Paladin:
The paladin summon is the best one to add some damage to the hunts , they hit a nice amount of damage and can hold some damage.
Knight:
Is on my opinion the worst, but if you are EK and you are hunting alone maybe it can help you to kill a little faster.
All Summons have an inconvenient, that in team hunts they are not recommendable since they can split pulls , so you will kill slower and that's very bad for the exp/h , so in my opinion they are only useful on lower levels or in solo hunts in some cases.