But seriously...
You can find a lot of different answers out there, but in the end, this is your system, so you will need to make the choice that is right for you.
My advice is to find the absolute best Front 3 Speakers you can allow yourself to afford. I would recommend these three be the same model (for example, all Monitor Audio Silver or all KEF Q series).
(This is an area with shades of gray... you can absolutely mix and match, but this can be tricky if you are not buying speakers that perform the same and have a neutral SQ.)
Anyway, These are generally considered the main Speakers you want to have match as closely as possible. I like to have my Surrounds match, too, but this becomes much less important. Rears, a little less important again (perhaps), and then Atmos/ceiling speakers... frankly, they really don't need to match up.
My personal caveat is, however, that I want Neutral and accurate Speakers all around. If your Speakers are all pretty neutral in SQ, and all have an accurate FR, it is easier to mix and match.
Lastly, if at all possible, it is becoming a little more in vogue to recommend a vertical Center using a matching Tower, or Standmount, as this can actual work better than a more common horizontal Center. That said, though, the Center Speaker is very important and if you must have a Horizontal Speaker, you should look for a 3-way W-T/M-W design as this will (most likely) give you a better horizontal dispersion than many other designs, meaning that everyone across your listening area is hearing the same thing.
Hope this helps. Happy hunting!