Canon for compacts and camcorders. Nikon is the SLR choice of the pros though.
Professional what? Professional Poseurs? Huh, I guess the three photography studios I've been to in my area that have multiple photographers and large studios that do photo shoots for universities and all the schools in a six county area aren't professionals since they're using Canon cameras. I can sure tell you all those people who look at their pictures go "OH MY GOD, someone took these with a Canon - I can somehow (Magically?) tell the difference!"
Image quality between Canon and Nikon with DSLRs are COMPLETELY indiscernible - if you say otherwise you're just lying to argue. I'll agree to that. Take two IDENTICAL photos with similar featured cameras (Two base models or two top end - not top end of one vs bottom end of another or anything) and scale them to the same size - in a blind test you won't definitively get a consistent answer. A photo journal did one in the late 80's between Canon, Nikon, Minolta, and I think one other - none of their readers could tell. The only difference between brands is price, build quality, and how easy it is to use and outfit. It's the same today, it hasn't changed - it's just digital instead of film now. I have a cousin who has had three Nikon cameras and all of those POSes broke and she couldn't use them anymore. I think she has a Samsung camera now or something. My father still uses a Canon Powershot he bought in I think 2001 or 2000 and pictures still look great and it works good as ever, just not 12 megapixels or anything (2 to be exact). Cousin bought her first Nikon in 2003 and went through them and had to buy a new one in '04, then in '05 and for awhile she just used her cell phone for pics (I never said they were picky on quality...)
This is the problem I have with
you Nikon people - if anyone ever asks about cameras in even a general sense the first bash some idiot always has to quip is "HUR HUR NIKON FUR DE PROFSIONALL CUZ I TAK PRO PICZ OF MAH KAT !!!!11ne1337!" whereas I don't see Canon people starting it (at least on average). I wouldn't have said anything about Nikon if some idiots on the front page didn't feel the necessity to do just what I said they always do. It's the same problem you get with Mac users. They pop up out of no where like little trolls "HUR HUR MAC R TEH BEST HAH I IZ L33tZ WINNR!!1!1on1" even though no one asked for their snarky little comments. Stupidness like this means no respect for you, and since silly trolls never learn it will continue to happen.
Besides, Nikon cameras are cheaper than Canon on average because they're cheaper built. Entry Nikon DSLR is 6.3 megapixels, entry Canon is 8 megapixels - when we're comparing new DSLRs this does begin to matter as downscaling will have higher quality the larger the RAW image. I prefer Canon's method of grading quality of lenses better too, Nikon's don't make sense to me - not that I care all that much since I won't own one. It's easy to tell the highest quality Canon lenses are the L-series typically with the white and red on the lens.
But I've come to realization that much of society is so foolish they need to assert their superiority to you in anyway they think possible, even if no one cares or if what they assert as a sign of superiority is simply a difference of opinion. Someone will say "Hey I just bought this new car and I love it" and the "better" person will come by and quip "HAHA, my car cost what three of your cars would - WHAT ARE YOU POOR? HAW HAW HAW". It's this self-believed superiority complex that so many people have that they can't STFU about what stupid BS they think is better. How about a thread asking a question about a PC issue? "HA you should've bought a Mac - I obviously have more money than common sense and it's what I did and TV and Movies say I'm cool if I do it so take that you conformist - I'm so different because I assert my difference by doing the same thing all the other people who are different do". It happens with cameras, computer stuff, cars, everything. This idea of difference is simply conformity of non-conformity - even though it never amounts to anything, the bloody fools.
I'll sum it up with a picture that captures this concept nicely (I've rambled [ranted?] along far too long anyway, but I'm famous for long posts - anyone want to tell me I'm inferior for using a membrane keyboard? Here's your chance...because I love typing on mine)