I personally recently purchased the GIGABYTE GA-Z270X-UD3 motherboard as my first z270 board. I have the same cpu as you, 7700k and I found the bios very easy to pick up on. I switched from Asus boards, specifically the z170 S, not because of any issues but simply because I liked the look and features of this particular board for my needs. Within a few seconds I had my 7700k overclocked to 4.6ghz and have had zero issues. Could I go higher on overclock? Yes but I have no need to. I like Asus boards but if the bios is close to what was on z170 boards with the new z270 boards then I suppose it will come down to which board fits your needs price and visual wise.
I've recently purchased my first Z270 board as well, GIGABYTE Z270-SLI, along with an i7-7700K, and for the life of me I can't make heads or tails of how to properly work the BIOS in my favor.
I've had an Asrock P67 board for the last 6 years and loved the bios controls with it, everything in pull down tabs etc. etc..
Now I have this board and everything seems to need to be manually typed in and I'm not so hot at it yet.
All I'm after is for the CPU to run at 4.5 (Right now) and to get my RAM to run at proper speed...
Do you have any pointers to give?