Only really to expand on Gráinne's comment as regards the 'collecting' and 'roster development' sections - which are, as said 'distinct' although they are intrinsically linked - I would like to point you in the direction of the in-game Achievements > Battle Pets > Collect tab. There are a series of achievements called Raiding With Leashes, pretty much all of which can be completed via the auction house - if you have the gold/inclination - or by completing old raids.
I used Zygor for legion and BFA, used AA on an alt for BFA. Personally i like Zygors format more. I like being able to target things like achievements. I used Zygor to get my Mindworm and my Lucid Nightmare as well as finish the Rep grinds for the allied races. I have zero complaints. My experience was great. I also used Zygor for some professions, recipe acquisition, a couple mounts, all of the Suramar quest line. Thank God for that. And for the last zone of Draenor on my Demon Hunter.. i forget the name.. Whatever the big daily hub thing was called.
Thanks so much for the replies. I think I am somewhat of a collector/roster builder. I go around doing the dailies but I also like buying pets just for their looks. I watched hazelnutty on youtube last night. I think I will focus on doing the expeditions when I have time to get all the pets that come from that. Then I will go back and do old raids like Eekwibble suggested.
Bioelectric Blast (Deadly) - Blasts the target area with electricity. Inflicts 65,654 Nature damage to enemies within 8 yards of the impact and creates a patch of Electrified Ground. Electrified Ground inflicts 14,882 Nature damage every 2 sec to players within it. Shock Burst (Important) - Inflicts 4,377 Nature damage every 2 sec for 12 sec. Upon expiration, strikes all players, inflicting up to 26,261 Nature damage. This damage is reduced the further away players are from the blast. Electric Discharge (Healer Alert) - Wekemara discharges electricity from itself. Inflicts 13,131 Nature damage that chains to additional targets every 1.5 sec. Submerge - Upon reaching 50% health, Wekamara will submerge and summon Spawns of Wekamara. Electrified Splash - While submerged, Wekemara rains electrified water from its pool. Inflicts 21,885 Nature damage to enemies within 3 yards of the impact area. Spawn of Wekemara (Damage Dealer / Tank Alert) Charged Bite - Inflicts Nature damage to an enemy Conductive Spittle - Inflicts Nature damage to an enemy and increases Nature damage taken by 50% for 16 sec. Loot Tables