With the offensive player that Lyles currently projects to be, this is a question that may have to be answered down the road, but unless it's in a deal for a potential superstar, I hope the answer is neither.
With Gobert looking susceptible against small ball & certain matchups at times, keeping all 3 gives Utah a solution to almost any matchup problem that they may face in the frontcourt.
Unless Utah is able to acquire a generational talent, which is unlikely, their best opportunity at putting together a championship caliber team will seemingly rely upon their ability to put together a deep, flexible, defensive oriented team that compliments eachother well.
Barring an unforeseen acquisition, they are likely going to have to take a "the whole is greater than the sum of the parts approach" & having the best 3 man frontcourt rotation will go a long way towards accomplishing that.