On his own category team Jiren is a main rotation unit, he has no trouble being consistent thanks to the Tournament of Power link and he can be either paired with Goku (Ultra Instinct - Sign-) or with Kale Berserk/SS2 Caulifla/Kefla depending on who you have.
Jiren's Super Attack is pretty standard, immense damage a lowers enemy's DEF. The 12 Ki multiplier is also the standard 150%, same as Goku (Ultra Instinct -Sign-)'s.
Jiren's Leader Skill is incomplete, as of now it gives his category 2 Ki and 120% to all stats with the addition of a mini Leader Skill for STR type.
Jiren has a very good Passive already, a 120% boost to both ATK and DEF is the same Unparalleled Golden Ki Super Vegito gets and he is not even awakened yet. In addition to this Jiren also has a medium chance, around 33%, to stun the enemies at the start of turn.
Jiren notably lacks Prepared for Battle, which would have been useful for Super STR, and does not really have anything that makes up for that aside from Tournament of Power, which is basically useful just on his own team. Hero of Justice is a very powerful link, but it's difficult to activate and Infighter and Cold Judgment are also very niche links. This unit's links are not bad overall, but they are definitely underwhelming.
Toppo is a very good support unit and the best partner of Jiren. Sharing both "Tournament of Power" and "Shocking Speed" can guarantee Jiren an automatic Super Attack under a 3 Ki Leader Skill; in addition to this Toppo can also activate "Hero of Justice" and add a 30% ATK and DEF boost with his Passive for Jiren.
This SS Gohan (Teen) is a unit obtainable from the World Tournament GSSR banner, he is an amazing support unit that offers 2 Ki and 25% ATK & DEF to all Super types and can also activate "Hero of Justice" for Jiren.
Jiren and Goku (Ultra Instinct - Sign-) share "Tournament of Power" and activate "Godly Power" for each other. When Jiren will awaken "Fierce Battle" will also be added to the links shared.
Jiren is a STR type, meaning his best investment is going to be lv.20 Critical and lv.6 Additional. Thanks to the huge DEF boost this unit receives from his Passive, no Dodge is needed at all.
Should I use Elder Kais/Grand Kais?
There is no need to rush and max out this unit's Super Attack, other images of Jiren were recently shown with a different art, so it's likely that he is going to be a farmable character either from a Story Event or from his own Dokkan Event. Jiren is already worth 9 Kais, but I would advise to wait and see.