If you opt for Ubuntu:
Ubuntu is in some ways built to act like a Mac. Run tabs, clock and other controls are on the top of the screen, which includes both top and bottom panels. Recycle bucket in on the bottom panel - on which open windows display.
Kubuntu (another flavor of Ubuntu) is organized much like Windows. One panel on the bottom, and the equivalent of a “start” button on the bottom left, from which pops up your menu options - if you’re currently on a Windows version, it will be almost instinctive to use.
There are a couple other more specialized versions - something called “Xubuntu” and also a netbook version.
If you’re installing any of them, on an older machine with more limited resources, there’s an alternate install version available at the download sites, which can install even if your system has limited RAM.
I have Xubuntu on several machines. It uses a lighter-weight desktop (XFCE) than Ubuntu (Gnome) or Kubuntu (KDE). Its one downside is the plethora of configuration apps -- a bit of a mess.