Hi Peter,
I can only offer my personal opinion on such matters.
The Nikon Coolpix range are excellent cameras all round. Due to their small lens diameter they are ideal for digiscoping use. You can also use them with supplementary lenses such as the EagleEye Optic Zoom, a 5x extender lens which can give superb results, but you still have that stability problem of using a longer lens and the need for a tripod.
The Olympus C2100UZ and Canon Pro IS90 share the same high quality Image Stabiliser and 10x optic lens, which is much more versatile in that the camera can be hand held. However the lenses are of a larger diameter and less suitable for digiscoping use. Also they fall in the 2-3 mp range and really you need something more like 5-6 mp. Both cameras are discontinued, though can be picked up second hand. I find it amusing that the C2100UZ's on eBay fetch prices £120 dearer than I paid for mine new a year ago. I think Olympus made a mistake in withdrawing that camera.
I have several friends who, lucky for them, possess the Canon D60 which provided you can afford the lenses too, give outstanding results. Certainly the best that I have seen, but then I have had a sheltered life

Due to it's size it would be unsuitable for digiscoping or for humping great distances on foot.
If I had the money, I'd have the D60, 400mm lens plus 2x teleconverter.
Having said that, in six months time no doubt there will be even better specified digital SLR's on the market and prices may begin to drop.
I know I haven't answered the question that you asked, but really the cameras shouldn't be compared directly as to which is the best. They are all good at what they do. I'd be happy with mine if only it was a 5 or 6 mp instead of 2.1.