The question about "assembly oriented or object oriented" doesn't make any sense. An object is nothing more or less than a collection of data. Assembly is just a programming language.
are handheld consoles more assembly orientated than object orientated?
Also I love Nintendo consoles ( Wii, gameboy, 3DS ) and PS2. Which of these is more accessible to program for?
There are programming languages that are a more natural fit to some devices, but you can use any language that compiles to the target architecture. Consider even a smaller device, the old Nintendo DS, that gave you a 66MHz processor -- many games ran at 30FPS, giving 2 million cycles per frame. You can do an awful lot of processing with two million cycles.
As for which is easier, usually the smaller platforms are easier to develop for simply because they are smaller. For the devices listed, there are several active GBA homebrew communities. The other platforms are going to be much more difficult to develop for just because of their relative size. PS2 and Wii are a pain to develop for even on the ligitimate devkits, and I don't think 3DS has a homebrew route yet.