I think in today's NBA it's all about which tool for which job. There will be times when Kanter will start, there will be times when Daniel will start. Then there's going to situations where we have Timelord or Baguette or even GWill in that 5 spot. Unfortunately we don't have a player who is a one-size-fits-all so it's going to be a horses for courses type thing I think. So I advocate keeping all of them 
If we had to choose who to ship out, I think it would depend on who we would be getting in return. That said, Kanter is getting paid more, so we would conceivably get a better return for him than for Theis.
I'm all-in on the center-by-committee approach. I think each of these guys brings something very useful to the court and we are going to be fine using a match-up based strategy at the 5.
Heck, you forgot to include using Smart as the occasional '5th' guy in some situations.
There really just isn't any real needle-mover out there that Danny is likely to get who is going to give us some great boost at the 5 over our current guys without having to risk weakening some other aspect of our roster. You aren't getting a 'star' big man without moving one of our starters. And just consider:
Jaylen can't be traded this year because of the extension.
Gordon is difficult to trade unless he exercises his option for next season already.
Kemba just signed with us -- trading him would be crazy weird and would make no sense since it would just create a hole a the 1.
Jayson is kinda the only starter who we could really trade -- but the Anthony Davis trade is long gone and unless you get a KAT back for Tatum, I just don't see it happening. He still has two more seasons on his rookie deal (including this one) and all signs are that they plan on giving him a max extension so I expect Tatum to be in green for the next 7 seasons.
So really, folks need to just get used to the center-by-committee approach.
Just enjoy, folks.