Ah, you'll be wanting to book in for IM Wales then! (possibly the only IM with over 100feet of climbing in T1 alone!!!)
But seriously though, Outlaw in Nottingham is generally regarded as one of the flattest around (although bear in mind flattest doesn't necessarily equate to easiest, as a flat bike means no respite from pedalling and is often more prone to the wind).
I did Maastricht this year but not having done Copenhagen I can't really compare, but my thoughts on Maastricht are:
Swim: Straight forward up and down in the river with a quick Australian exit at the turn point. Upstream for first half, although flow not really noticeable against, but definitely does give a faster second half though on the downhill leg. Nice enough, somewhat murky round the Parliament building though.
Bike: Bit mixed really, Probably best described as gently rolling with a couple of 'hills' but nothing spectacular (although FOFF hill did nearly kill me on second lap). As mentioned before though let down a bit by a lot of tight turns and some poor road surfaces (concrete slabs, and cobbles ... oh those bloody cobbles!).
Run: Best bit of the race. 4 laps through the city (with a nice detour through a park for a bit of 'reflection time'). The support on the run course is phenomenal, the people of Maastricht really turn out and every half mile or so there was another raucous street party going on to keep you going. (and the Dutch really got in to the 'piraat!!!' vibe )
Overall setup: Organisation was top notch with Swim, T1 and T2 all in the same place, and only a short walk from the finish line. Finish itself was in the town square which again provide for excellent atmosphere.
If you can deal with the shortcomings of the bike course (and its only certain sections of it) then I would definitely recommend Maastricht.