You new to water cooling? It is fun...can be a bit expensive...but good fun and a silent cool PC is a joy...you will enjoy it.
At the end of the day all these boards can be water-cooled just come prepared in different ways....like no prep...partial prep....full.....the choice for oc level is maybe different too...though an average oc will be perfectly possible on all of them too.
So it comes down to your main passion a bit. If it is pure maximum oc then the apex. If mainly gaming then code...formula. If you want gaming and oc bells and whistles maybe extreme....comes with full block.
I may have to check out extreme. I went with formula because I thought the aesthetics better and I wanted my own block etc...but...on seeing it I realise the EK vrm block is badly designed....wont accept fittings for larger diameter fittings...a design flaw in my opinion..since i have larger diameter tubing and fittings...but for a new build less problem since you can go with the fittings from the start for the whole build...
Research is key i guess I'm saying...for exactly what you want out of the board...
I can see myself trading formula for extreme.... once it arrives....when is that?
Tuf...not sure really...always seen that line as a bit of an aesthetic choice more than features difference...maybe I'm wrong but it seems like a "military" code or formula equivalent.....certainly water-cool-able and certainly give you oc headroom....just maybe not the last percent of oc performance that extreme or apex will give.
Apex sacrifices all for ultimate oc...