Im open to discussion
@David Analog , what are you thoughts?
The XS-65 is the least expensive Wetsounds 6.5" coaxial while the M650 is the most expensive JL Audio 6.5" coaxial. I found that odd since they don't compare head to head.
The newer Wetsounds XS-65i is a GIANT improvement over the previous XS-65. This model went from an erratic W-dome tweeter to a smoother true dome tweeter. It was actually Earmark personnel who brought this to the attention of Wetsounds and recommended the tweeter change. So don't get the old model from someone's old inventory.
The XS-650 has a larger midbass driver voice coil and larger dome tweeter diameter & VC over the XS-65i. So there is a difference in power handling that you want to properly match with your electronics.
The JL Audio M650 has a larger tweeter but a smaller midbass cone surface area than the MX650 model. On balance, in a speaker no larger than a 6.5", I will take the larger midbass cone. I consider the M650 a bit of an odd duck.
Comparing the Wetsounds with the JL Audio becomes more subjective. Both have top-of-the-line marine construction. Both have good midbass. Past that, they sound very different in the mids and highs.
The Wetsounds uses a hard metal dome tweeter with a 1st order highpass filter. This speaker is voiced more aggressively in the treble and gives you a little extra kick on the upper harmonics making the speaker sound more distinctive and giving you a little extra sizzle when underway and competing with the wind and noise.
The JL Audio uses a lower resonance soft dome coated silk tweeter with a 2nd order highpass filter (double the slope). This speaker gives you faithful reproduction with the smoothest midrange and vocals.
Comparing specifications between different brands is useless because these are unqualified specs and you don't know what standards apply to sensitivity, power handling, frequency response, etc. etc. As an example, is the efficiency taken a 2.83 volts or 1 watt ?, one foot or one meter ?, peak or weighted ?, on so on.
Nothing can compare to an audition in person.
People will choose based on preconceptions, brand bias, a sound signature that they are more familiar with, whether correct or not, or any number of subjective references. Both Wetsounds and JL Audio coaxials are winners.
You might get with Odin @ Earmark Marine, which is listed in the vendor section. Odin is an authorized on-line dealer for both Wetsounds and JL Audio. You won't find a better resource when the installation begins.