I've been tossing up between all the superzooms, SX1, SX20, Pana FZ35 and Sony HX1. I think in the end it just has to come down to personal preference & price - the image quality is pretty similar across the board (which is to say, noisy in low light & noise reduction visible even at base ISO, but that's only if you're a pixel peeper).
The SX1 & HX1 have the advantage of the CMOS sensor which lets you get a better 'burst rate'. I think the HX1 goes up to 10 frames a second without dropping image quality. Whether the CMOS actually gives you a better picture, however, is pretty debatable. When you're working with the teeny tiny sensors that you get in the superzooms, going CMOS over an optimised CCD really isn't going to give you much of an edge.
The SX20 and FZ35/38 were the joint winners of the DPreview super zoom group, with the FZ35 being lighter and a smidgen 'faster' at the long end of the zoom, while the SX20 has better colour and the advantage of a hotshoe. In regards to image quality between the two, you're standing on pretty even ground. The SX20 is a bit 'softer' but its noise is pretty close to resembling grain and its even throughout. In comparison, the FZ35 is sharper, but that sharpening occasionally creates some nasty little artifacts. Both cameras have a similar amount of chromatic aberration at the edges, but the FZ35 does a very good job of correcting this in camera. The FZ35 will also output to RAW where the SX20 does not, however it's worth being aware that you'll then have to fix that CA yourself.
In relation to handling, the SX20, SX10 and SX1 are all pretty much the same - they're quite comfortable in the hand and have an articulated LCD. The usefulness of the articulated LCD is debated and more in the style of a movie camera than a film camera. The FZ35 is a fair bit lighter, but that may not be to some people's tastes and its LCD is fixed. The Sony HX1 is a bit chunkier than the Canons and I actually found the grip quite uncomfortable (I have smallish hands and my fingers weren't long enough to wrap around it securely). While I'd normally prefer its version of the articulated LCD (since it pops out horizontally, so it's good for above head or waist high shooting) it seemed to protrude a bit from the camera rather than sitting flush against it, making for an even clunkier design.
So, at the end of the day, its really about what feels most comfortable for you and what features you prefer. Do you really want to shoot in RAW? Do you really need a hotshoe? Are you wanting to take lots of photos in the span of a second? Would you prefer something a bit lighter and easier to handle?
The image quality across the board is so similar that it's really hard to make a decision just based on that (believe me, I've tried!). So long as you're aware that you're just getting a standard point and shoot with a long zoom, you shouldn't be disappointed.