Well, yes, this question gets asked a lot and people will recommend this or that distribution and they all have reasons to suggest a certain choice. What I'd say, though, is that you should probably consider it from another point of view. Ask yourself (or your friend) what exactly you are looking for. If that thing is maximum ease of use then you have a very wide range of choices (see this DistroWatch search.
What you may want to ask yourself is the question of which Desktop Environment to choose, i.e. whether you want maximum UI familiarity with Windows 7. If your friend shudders at the thought of developing completely new habits then you don't want to bestow a distro with a completely unfamiliar interface on him.
So the question seems to boil down to the choice of DE. Obviously this is a very subjective matter but I'd suggest trying something with Cinnamon (like Linux Mint which is the parent project of this DE).
KDE might be another good choice for a Windows-like desktop (with Kubuntu or Linux Mint's KDE edition).
My personal favourite would be MATE (again with Linux Mint or Ubuntu MATE edition), which by default has a slightly different layout than Windows users are accustomed to but can be easily tuned to resemble Windows experience.
If you want to go with a very lightweight option, you may want to consider something with XFCE or LXDE (Xubuntu or Lubuntu, respectively).
There are also two popular DEs: GNOME and Unity (the latter used in main Ubuntu edition), but those two are rather far off in terms of Windows UI familiarity.
One more suggestion: there is a distribution called Zorin which boasts a user interface that resembles certain other systems and you can even easily switch between them with a "look changer". The "looks" include Windows 7, Windows XP, Windows 2000, Ubuntu Unity, Mac OS X and GNOME 2. Some of these are premium features that need to be paid for but I have no idea how much that costs.