I have several exercise videos,...is it best to stick with one for a few weeks, or can i just use a different one everyday?

Ideally, you'd want to have a mix of exercises, but that doesn't necessarily mean a different video every day! Perhaps you can group your videos into loose categories, such as cardio/strength/flexibility and further break those down into types, like cardio-kickboxing, cardio-step, and so on. You want to ensure that you're not doing two strength workouts on back-to-back days in order to give your muscles a chance to repair themselves, and you can mix up the cardio styles to prevent overuse.

However, one of the benefits of keeping the same videos on the playlist for a few times (as opposed to just once a month), is that you become familiar with what's coming next and can focus on keeping the momentum going in cardio or lifting heavier weights with each successive week. A compromise might be to rotate in 2-3 of each type of exercise video every few weeks so you can get the benefit of working at your hardest while not getting bored too quickly.