They are all good and all worth developing

Apoth- i use in fireknight and sometimes in spider, and have used on dragon too....strongest in fireknight in my opinion but good everywhere

Achak- is brilliant in spider, top tier spider champ without any doubt.

I dont have deacon but i wanted him badly for arena for a long time, he is considered top tier just about everywhere i believe.

All of them are good, and we probably need to know more about what content you are looking to improve on, such as Dungeons, clan boss, arena, etc.  The reason being is that some champions are better at certain things than others

For what it's worth, I have found Deacon to be very useful for both Dungeons (all of them) and Arena, so my money would probably be on him if I had to choose

You say:

If you need to know the rest of my team it is Alika, Crimson Helm, Kael, Sniper 

So you probably think you have one team in this game, doing all the content. But that doesn't work. You need different champs with different skills to win in all locations of the game. You definetly need more than 5 champs in this game.

The first thing you should do is to build a champ that can farm exp for useless uncommen champs you level up as food for your real champs. Kael is good in this farming job. Find a stage in the campaign where Kael can do the hole job alone and put 3 useless uncommen at his side to gain exp for them until they are at maxlevel. Increase their rank and repeat - until you have enough champs to level up your Kael. He should get to level 60 to do his farming job even faster and better. Then you can increase the level of your other champs faster. Apothecary and Deacon are both great and should be your next lvl 60 champs after Kael.

You  can't  really  conpare  any  of  them  because  they  do  completely  different  things.  Apothecary  is  the  only  healer,  Achak  is  the  only  Burn/CC/Defensive  Buffs,  and  Deacon  is  the  only  Defense  Down/Leech.