Opinions on Solid States vs M.2 drives?

I think you are confused. M.2 is the interface to Solid State Drives, just like SATA. So you can have SSD with either SATA or M.2, with M.2 having higher Read/Write speeds compared to SATA. The only drawback for SSD is it's finite write life cycle.

If you can afford an M.2 drive it is definitely worth it. The speed is really nice and it is aesthetically pleasing.
You can always look up speed benchmarks and decide for yourself if it is worth it or not.

Well, I have 3 drives, 1 HDD, 1 SSD and 1 m.2.

I use my 256GB m.2 NVMe drive as my boot device (Windows). I use it so that as soon as I press the power button, literally 3 to 7 seconds later I'm in windows and can immediately open programs or browse the web.

I use my 1 Terabyte Samsung SSD for game storage, any and every game.

Finally, my 1 Terabyte Hard Disk Drive is used for random non-essential storage.

Long story short, if you want to boot windows faster than a 5400RPM or 7200RPM HDD, buy a cheap 120GB/128GB SATA III 6GB/s SSD and install windows onto it. If you want even faster boot/load times buy a 256GB m.2.

if you want gaming with the ssd a sata ssd is fine, I have buy a m.2 evo 970 from samsung think that games could load 3k Mbps and I was wrong, the only difference is the windows startup :/

jfyi nand flash performs more efficiently when warm

You can really feel the difference between M.2 and SATA SSD when you make it as boot drive. Try it out and M.2 will definitely feel like heavens.

Took a external ssd apart as it was a m2 drive with a sata interface.. got a external 500g ssd for 80 bucks.. and rip it open and install it as a m2.. best choice ever

M.2 is worth it if you can afford it, though it is quite a bit more expensive than an SSD most times.