Vu+ Ultimo 4K. But also Vu+ Duo4K or Dreambox DM920.
The main difference between Ultimo 4K and other mentioned boxes is that Ultimo can accept 3 physical tuner boards.
Duo4K and DM920 have only two slots, but one tuner can be a double one in a single card, so you have always 3 tuners available.
I have one Duo4K and one DM920 and both are very good receivers.
Just a recomandation: keep attention to choose the right tuner card! Not all cards are DVB-S2X compliant. To choose the right one, check the chip type, it must be Broadcom 45308.