USB or 3.5mm Headset? Which?

usb headsets tend to have less hissing.... not necessarily. sometimes the usb bus can introduce hissing on usb mics that is not apparent on analog mics. it can swing both ways there as usb can sometimes be better than 3.5mm while sometimes 3.5mm can be better than usb.

its a misconception that onboard audio is bad. many onboard audio chipsets are fair and good enough for most people to use. normally when users ask about soundcards i suggest trying the onboard before spending any money on a soundcard unless it lacks features they want. if you do need a soundcard you can get one for $27 which is a bit better than good onboard and should eliminate noise if you had any.

usb or 3.5mm? depends on preferences. usb includes its own dac and amp inside the headset (a soundcard inside the headset) and bypasses onboard. good if you have a laptop or no soundcard and do not want to upgrade the onboard though if your system is known to have any issues with its usb it might not be as nice as 3.5mm. 3.5mm is better if you have a nice soundcard as you can take advantage of its features or if you have known issues with your usb causing static or hissing sounds.

best headset for cheap is likely the hyper x cloud or hyper x cloud 2. best option under $100 is likely the hd518 headphones paired up with a clip on or boom mic. you could even add the xonar dg soundcard and push just a bit over budget but it would be a good setup.

if you do not want to deal with soundcards at all, i'd go usb although some of the nicer headphone/headset options are 3.5mm. your choice.