I am using both of these with identical pairs of Polk RTi28s, the speakers Dennis Murphy recommends redoing the crossover. I haven't gotten around to redoing the crossovers yet.
To put the conclusion first, I definitely prefer the Panasonic XR45.
The SD-SG11 changed rapidly during the first 30-60 minutes it was powered on and got better and better, but no real change I can detect after that. The bass is very tight and the sound is clear and detailed, compared to my old SS stuff. Based on that experience I got another one. One went to a bedroom and the other to the living room. It is a great all in one system, has minidisc and CD, and the build quality is excellent.
For our main listening room, however, I chose to get an XR45. I installed it and it sounded OK, not as good as the Sharp. I was disappointed, but knew from reading the posts that the Panasonic took a long time to be its best. This is completely true. I ran it all the time in party mode and after about 30 days it was way better than the Sharp. The sound is smoother, the imaging better, and I like it better. Unfortunately, something went wrong on one of the boards about 2 months in, since the right channel was down about 1.5 db from the left and I couldn't get it to balance right. Panasonic put in a new board under warranty in just 3 days(!), so unfortunately it is back to the original sound right now and burning in again. It is tough to wait for it to sound better. The tuner is better than the Sharp also, if that matters to you (it does to me).
If more details are needed, I'd have to do an extended comparison looking for what you are interested in. Unfortunately, I've been too busy to listen much at all. My family gets to more than I!
By the way, the Sony all-in-one first generation I tried was much worse than these two. I also like the budget buy both of these were: the Sharps for around $150 and the XR45 for $245 refurbished in black. You can probably tell that I'm going for budget quality sound and this is the best I could come up with given available components at this time.
Hope this is of some help.
Ben