A lot of people agree that 1080p is the best res for a 24" monitor, though some do like the same res on a 27". Others say they notice distortion with 1080p on a 27".
IPS panels are more expensive, but give better color and image quality. TN panels will give you better gaming response and are generally cheaper. If you don't play fast pace FPSs, your response time will still be fine on an IPS.