I'm equally comfortable with trad and matched. For swinging Jazz, I prefer traditional. The left hand in bebop is used completely differently than in other types of drumming. The left hand is used to "comp" with the soloist. The strokes are almost exclusively grace notes. I find this to be much easier to do and more natural with traditional grip.
Have a look at videos of drummers who play bebop with matched grip. Their left hand just looks odd to me.
http://www.youtube.com/watch?v=eQuDAhMXwQA - this is not standard "matched grip". Or how about Ari Heonig:
http://www.youtube.com/watch?v=7g0dE6Y-1uk - his "technique" is painful for me to watch it's so ugly.
FYI: If you want to see an excellent discussion of the dynamics of traditional grip, Steve Smith talks about it, I believe in the "History of the US Beat" DVD.He refers to the traditional left hand grip as a more 'caressing' type of grip.
I guess I would agree to a point. I don't know if I am in agreement about the snare always comping aspect. Granted that happens way more in jazz than any other genre but I'd point to Bill Stewart, Tony Williams and Jack DeJohnette as players that are way more physical with the snare than just ghost note comping. Different than say Jimmy Cobb.
I grew up using traditional and switched to matched in the '80's when I was in college. It was considered the smart move especially when you were also playing mallets, multiple percussion and timpani (where the terms French and German grip are talked about in terms of tone).
I now play mostly matched. I also find my jazz brush work always feels better with traditional. But there are two issues that interfere with me giving a blanket affirmation to using traditional for all things jazz.
The first and most important is that the angle of my snare is directly connected to my ability to comfortably play rim shots. I also had a discussion with Dave Weckl one time at a playground where our daughters were playing back in the '90's....he's local. I mentioned that I'd have to change the angle of all of my drums and cymbals at least in some way to effectively use traditional grip and pretty much commit to it for the majority of my playing. He agreed with me on that and said he had made adjustments, especially after studying with Freddy Gruber.
I can go back and forth between the two grips but feel limited, especially on snare, if I am using my standard flat or mildly angled (down toward me) snare position. If I am going to use a traditional grip, I feel I have to commit to it comprehensively and adjust my drum set. The big guys that do go back and forth (Weckl, Smith, etc.) seem to play traditional mostly and
occasionally switch to matched. Not usually the opposite. The only exception being Bill Stewart who plays matched all the time except - for when he uses brushes.
The second issue is that I am always more comfortable playing matched when I get down to the floor tom, especially if I am using two floors (14 and 16 inch). I just feel like I have to torque my body more when I use traditional. Granted Vinnie, Dave and Stave don't seem to have this problem but for me it makes me more 'snare centric". That may be OK for jazz but not for pop/rock/funk. When I'm playing matched the grip seems to turn more gracefully depending where I am playing on the drums set. It can morph between French (thumbs up) and American/German (thumbs to the side). That just feels more organic where when I was first studying drums the way to get around the set included turning the traditional left hand over to play floor toms. Just never felt natural to me.
I do keep up my traditional grip on my pad and most of the time use it for brushes. However, I normally will play matched on the set, even during jazz tunes. My left hand may go to French grip for sensitivity and speed at low volumes (saw Bill Stewart do this). I will sometimes switch to traditional when my left hand is getting fatigued and I don't have to play rimshots. That's about it though.
As far as grips looking uncomfortable, I'll defer to an experience I had at NAMM back in the '80's. I saw Jeff Porcaro playing in one of these NAMM super groups (probably co-endorsees). He sounded fabulous as usual but looked
very stiff while playing. I learned a lesson after thing about it. He was playing like he would at a session. I figured that sometimes you have to add 'weight' to your motions to make sure they are precise, especially at slow to medium tempos. This was his way of making things lock. Don't know if this applies to jazz but I can definitely see how the mechanics work in general.
HTH
Jim