I've got the Panasonic FZ330 (aka FZ300), which offers 25-600mm (24x zoom) at f/2.8. If I'm taking bird photos, I put it in drive mode and snap off several shots at once to mitigate the effects of camera shake. I tried out a number of cameras, including the FZ2500, which I found too large to be comfortable. The FZ330 is just about perfect for me in terms of size, features, and complexity. There are also teleconversion lenses (of varying quality) that you can get for it to increase the reach even further, which makes it handy for identifying distant birds, or working out whether that blob is a bird or a molehill/hare/bin bag/chimney/etc. The moveable touchscreen is very useful, especially if you've got the camera on a tripod and want to quickly move the focus area, etc.
On the down side, it gets noisy quickly in low light, and trying to photograph distant hen harriers coming in to roost, hand-held, just before sunset was not a successful venture. :\
I found it very useful to go into a camera shop and try out the various models I was interested in, having read up on them beforehand. Even though I was limited to viewing images on the camera's built-in screen, I could assess the image stabilisation, zoom, drive mode, low/artificial light performance, and ergonomics. There are plenty of examples online of the best that all these cameras can achieve, but that doesn't mean much if the camera is too heavy to hold comfortably or you struggle to see the screen or you need to use a tripod to get decent images.