Of those two, I would go for the Panasonic. It is a tapeless workflow, but the images you get will be cleaner (generally) than the HDV from the XH A1S. On most current NLE's you can edit the AVCHD natively (which is nice) and easier than dealing with converting the HDV before you edit. If you have camera shops nearby, they might have demos of both cameras you can get a feel for them.
Hard drive space and SD cards will also come into play here. Plus whatever audio equipment/tripod/head/lights/etc you'll need. But of those two, in my opinion, the Panasonic is a much better camera.
Personally I went the DSLR route for now, but looking to invest in Red Scarlet once they have hit the market for several months. DSLR's are a bit of an investment in extra equipment to make them proper video-like cameras.... but I've tried to make purchases conscious of what I would be using in the future to fit those needs as well.
But thats not to say that Panasonic wouldn't make great artistic shorts. And if you are used to video cameras it may be easier to handle than the DSLRs, which handle much more like a still camera that just happen to shoot video.
If you had that sort of cash, I would certainly be looking at a Canon 7D. The 5D might be a little out of your price range, but I reckon you might be able to pick up a 7D for around that with a lens. Mind you, the 7D has a crop factor of 1.6?? Which means every focal length of lens you get, you will have to multiply by 1.6...but I did that for a long time with my 10D when it first came out. GREAT for telephoto shots, but wide angle - you need to buy wide lenses. I ended up with a 17-40L series lens and it worked great with my 1.6 crop factor.
I had a look at both cameras. The P2's have always been good. The canon's have always fallen a bit behind with the camcorders. But I believe the new range of SLR's have it over all of these.
I was watching a review of the 5D, 7D and a number of other cameras that were pitted against 35mm film cameras (the benchmark of the pro industry) and the quality of the 5D and 7D stood out especially in low light. the Canon cameras actually knocked the hell out of the RED camera in low light!
But in saying that, the Canon cameras do have a rolling shutter. That means that on fast pans, the image can bend a bit as the sensor tries to catch all the image. But that's easy to shoot around.
In my opinion, the SLR's are the way to go. 2 cameras in one, and you also get that beautiful 35mm film depth of field everyone loves to shoot with. The microphone sucks on the canon's though, but thats the same with every stock mic on every camera.