as i sit at my desk on the computer, it feels like really bad tension in my neck and shoulders which type of chair would be best for sitting at a desk?
I am betting that your chair is the wrong height which is causing you to have to hold your head either tipped back or forward. Your eyes should be level with the centre of the screen
You need to be sitting so you are all at right angles. Calves at right angles to upper legs, back at right angles to legs, forearms at right angles to upper arms. Screen at the right height for you. Have a look at the pic on page 6, this is how you should be sitting. http://www.hse.gov.uk/pubns/indg36.pdf
Adjusting your screen can make a big difference. I have mine so I look straight at it in front of me and my neck isn't bent up or down to look. I also try and make sure I sit up straight with my shoulders rolled back. You can get angled cushions to sit on and a lumbar roll to help you sit properly and adjust to make sure you can put your feet flat on the floor (or something).