First, think about the available amplifier power, room/listening area size, your musical preferences, and your preferred listening level. Consider whether you have a preference for horns or dynamic speakers, since they can offer two different presentations. At least be aware of the different driver, cabinet, and design choices, and how each may affect what you hear. Decide how important the level, quality, and dynamic impact of the bass frequencies is to you.
After considering the above, then purchase the speakers which sound the best to you, within the budget you have available. IME, you may experience better sound quality by choosing a pair of mostly full-range main speakers (down to about 40Hz) and then adding two (or more) subs. There are more speakers available that can deliver good sound down to about 40 Hz than can convincingly reproduce the lowest octave, which can be very expensive and difficult to do well. Having the benefit of flexibility in the placement, frequency, and level of two (or more) subs allows you much better control over the bass frequencies and ultimately much better bass in your room, IMO.