Well, i have visited many airports, to just go and watch aircraft come in and out it would have to be LHR, just because of the variety and that you get a clear view of 27L from the Queens building.
If there was more traffic at BRS, that'd be my favourite for just watching, sitting in the Lay-by round the back of the airport is just so beautiful and peaceful.
AMS is still my favourite though, and my favourite spot there is parallel to the Zwanenburgbaan where you have a clear unobstructed view of the whole runway, and quite close too!!!
No more than 50 Ft from the runway
Woah, slight Exaggeration there i think, if you were that close you would be hit by the wingtips of A320's and 757's, or smashed by the engines of a 747!!!!
I'd say that the closest a spot could be to a runway is 200m+ so there is not enough jetblast to knock you over, not to mention wings!!!!
The best spot at BRS is about 200ft from a Taxiway, its so close because the only aircraft that use it are no bigger than a 757, where the wings are nearly over the fence (which is only 4ft high!).