What LSB should I buy ?

The one you really want for endgame and don’t want to farm, or none at all. They are all equally overpriced and the only value is how much you give them. Buy the one you are going to use and enjoy.

Get the grand inquisitor, you get the most bang for your buck. 5 relic 5s instead of 4 relic 5s

Sorry. I am completely turned off by LSBs with the new price point, but here is an honest answer if you are set on spending the money.

Starkiller is a great team and if you already have jade and emperor palpatine it it could be worth it, but as far as I know offers little in terms of other rewards.

Aphra is a good option if you are looking to get into a higher end guild because sanos is used in platoons in ROTE and I’ve heard Hondo can solo new raid.

inquisitors are likely the best option for personal rewards as they can be used in conquest, and have an event battle.

none of them, just farm them, most likely any you add won't be played regularly, and new squads come along and become more useful... although if you had to choose one, I would suggest Aphra, one of my favourite squads (I farmed her as soon as she came out, was a bit of a grind as I am F2P, but i got there just as I will with Master Mace (after i finish GL Ashoka farm)