Why the Golden Jaguar suit instead of Black Panther?

There are multiple reasons, all of them connected with each other.

First, both suits represent the Black Panther. T'Challa's sister made both for him to wear, one flashy (to show off as a king), the other more subdued one. In fact, on his first mission, T'Challa wanted to wear the golden one since he was interested in it but since he was persuaded to wear a stealthy suit for the stealth mission, so he wore "the silver" one. I guess "The Golden Jaguar" is the name from the comics.

Second, Michael B Jordan's character Erik Killmonger was trained and specialized in the destabilization of authoritative regimes. In Wakanda, he gets there, disposes of the ruler, takes over. And what do we see him do with power he gains that way?

He shows off at first and for a good reason. Earlier, we see T'Challa wear simple, traditional clothes. Why? Because the people of Wakanda know him. They all know that he is the king and there is no need for showing off. Killmonger wears flashy golden clothes with US-style shoes and pants. Why? Because his power is not certain yet, he just took over. All of his clothes scream: I am in charge. I wear the crown, I wear the gold here.

It is easier to follow a king which looks like a king, thus the golden ornaments for the benefit of his subjects. And yet, it is easier to look and act authoritatively when you're wearing your own pants and shoes, clothes you're used to and feel comfortable in.

Third, he wasn't given much chance to pick a suit. T'Challa's sister steals the suit and some other equipment before the final battle. The only remaining suits are the old suit and the new golden one. Killmonger picks the golden one. Of course he does, because that affirms his power. No shabby old suit for him, but the newest and best, fit for a king.

Fourth, why he chooses to burn the flowers and change the traditions? Because that's what newly crowned dictators do! Out with the old, in with the new, just do it fast before anyone gets funny ideas to ask you "What the hell are you doing?" and stops you. History starts with a dictator. In a few years, nobody will remember how it used to be. And those who remember will be afraid to say anything because by that time the new leader will get a chance to stabilize and fortify his power. And by burning the flowers, nobody will get any funny ideas to overthrow him, to even think about throne succession after him.

We live in the now, where I am the king. My word is law, there was no past before me and there will be no future after me.