I am buying an ethernet cable that is around 20 meters and i want the best quality. I dont really care about the price. I dont know what type to get though. Should i get cat5 or cat6? Should i get STP? I am using the cable to connect to my router downstairs to my computer upstairs.
The only difference between Cat5e and Cat6 is that Cat6 adheres to higher standards in terms of cable crosstalk and interference. Unless you have a giant electromagnet or something Cat5e will do the trick.
you can get a standard cat5 cable for around 5$ where as cat6 will cost you around 6-7$ ,, Although price wont' matter but still, cat5 will be sufficient from most of the purpose.
Cat6 work for the speed upto 100 gb/s which means your router should also be compatible with the same. But in practicle situation you won't find your Isp providing speed in Gb/s .
Therefore there is no need for cat6 for now or for few years. I used cat5 to connect my system to router and it work fine.