The ideal window management would be most efficient with screen space and allow users to do window management tasks as quickly and easily as possible. However, there is often a tradeoff between these goals. This is my opinion of the best compromise:
Buttons
It really doesn't matter which side of the window the buttons are on. They should be ordered from least destructive to most destructive with most destructive the furthest away from the centre of the window. This means close, minimise, maximise/restore if on the left or maximise/restore, minimise, close if on the right. Most of the default user interfaces do this anyway.
Resizing
It is a poor design decision to have a border so small that grabbing it is really difficult to do. In fact, this has been marked as a critical bug by the Ubuntu design team (bug #160311). However, using a really thick border like in Windows uses up too much screen space. I think windows should retain the small visible border but have a larger, invisible border (nothing huge but enough to grab). Also, resizing can be made simpler using a shortcut key. I currently use compiz resize configured so that pressing the super key allows me to resize the focused window by simply by moving the mouse. I can then click once I am happy with it. I find this saves me a lot of time over resizing using the border, even if it is a thick border.
Moving
The almost ubiquitous drag and drop method of moving windows works well, so should be kept. It is a bit of a hassle moving the mouse all the way to the top window border to do this. The GNOME window manager (metacity) and compiz provide a quicker way to move windows. You press the Alt key then you can click and drag anywhere on the window. This saves time therefore it is good behaviour and should be kept/adopted. I'm not sure what other desktop environments like KDE, XFCE, Mac OSX and Windows do but if they don't already, they should implement this behaviour.
Switching
Windows are traditionally switched using a dock or panel. I find this works fairly well but not as the only method of window switching. Docks and panels should have the ability of window dodge/intellihide to save space. I find that plain autohide, like the kind currently used by GNOME panel is insufficient. Which side of the screen the dock is on doesn't really matter and should be a personal preference. I happen to like my dock on the left hand side. Docks can save space compared with panels by grouping windows and using icons instead of text. As my main method of window switching, I use compiz scale. This gives me an overview of all my windows from all my workspaces. I have it configured so that I click to choose a window and right click to close a window, making these actions very quick. Another advantage of scale is that it gives a better visual clue of what you are doing in each window so it is easier to know which to pick. Window previews, which compiz also provides, also have this effect but require hovering over the dock/panel items to get the preview, making it slower. I also find scale quicker than Alt+Tab because I don't have to flip between the windows. Scale can be activated using shortcut keys but I prefer to use a 'hot corner'. Corners are very quick to get to with the mouse because they are infinite in 2 directions, especially with a trackpad as this only requires a quick swipe of a finger. I use the bottom right hand corner because it is furthest away from most of the activity so isn't easy to accidentally activate. Obviously, this depends on where other desktop elements are placed, but bottom right is ideal for me with a left dock and a top panel. I still find dock items useful for actions such as launching and minimising.
Multitasking
Often it is necessary to view multiple windows at once eg. for drag and drop actions between windows. Overlapping windows work quite well and are optimal for dialog windows which only exist for a short period of time. However, tiling is far superior for reading from multiple windows or drag and drop actions. I find I have to tile manually which is tedious and it should be easier. I would like to be able to Ctrl+click on items in the dock/window switcher to tile them. By default these should take up equal space on the screen (or as equal as possible - 3 windows would be hard to fit equally) and should take up the whole screen but it should be possible to drag the border between them to adjust this. If a window is closed or minimised, the others should increase in size to take up the remaining space. A single click on any of the dock items should revert back to the normal windowing mode and focus that window.
Some of these solutions don't really work on tablets and other devices without keyboards. However, multiple gestures could replace some of the keyboard shortcuts. The interface should really depend upon the device it is used with. My suggestions are good for a laptop or desktop computer.
I find that the window management experience on Ubuntu with my compiz tweaks outweighs the others, although I have never used Max OSX. However, it is still not perfect. I think my proposals would make these window management systems better but it is not perfect and I don't think there is a perfect way. We are limited by our input devices. Maybe one day we will find a way to hook our brains up directly to the system but until then we are stuck with what we have.