When it comes to subwoofer choice, the decision is can be made based on the variables below.
Arguably the most important factor when considering a type of subwoofer. We recommend vented subwoofers for those who primarily watch movies. Our vented subwoofers have more output below 40hz, i.e., they sound louder when playing deep bass; they are also more fun/entertaining for your friends.
For 2-channel setups, we recommend sealed subwoofers as they tend to sound "dryer," a characteristic that lets more detail come through in music playback. This is due to a better transient response, where the bass has less decay in the room compared to the vented counterparts.
Now that you have an idea of the type of subwoofer best for your usage, how big of a subwoofer should you get? For our designs, budget permitting, you can go as big as you like; just make sure the subwoofer driver will be at least 10cm from the nearest surface.
That being said, if a smaller subwoofer will fit in better with your room decor or partner's expectations, it might be best to go with a smaller subwoofer.
Is there such thing as having too big or too many subwoofers in your room? Not necessarily. The key is to find out the best location/s for placement and then calibrate for the best in-room response. Just make sure that the number/size of your subwoofers don't compromise speaker placement or the main listening position.
Large or many subwoofers in a smaller space let each subwoofer work less, leaving more headroom available when dynamic peaks are called upon. You will also enjoy a cleaner sound as subwoofers that don't have to work as hard, play with less distortion.