Loudness depends on more than one or two parametres. Wattage is pretty poor indicator, although it is one part of the complicated equation. Impedance is misleading, as it is usually marked as one number, while it actually changes quite a lot depending on the frequency.
Listen to the sound, and choose the one that you like. If your choice depends on the specifications, do your homework and read the marketing stuff. Many of the meaningful parametres are not published.