You can tell the resolutions supported by the biggest possible audience back then by looking at the Workbench resolutions.
On a PAL TV (not monitor), the 320x256 appeared slightly squeezed vertically. On an NTSC TV (not monitor), the 320x200 appeared stretched to 4:3.
Many old US games artists drew their graphics to appear correctly on NTSC displays, which of course make them appear very squeezed on PAL TVs, since the vertical stretch the gfx artist counted on isn't there. One example is Zany Golf. I don't know any games made in Europe that compensate in this way for the comparatively close-to-square squeeze of PAL TVs.
UK games may have made 320x200 games to suit portability or support NTSC sales, but there's no reason to stretch them - since they were drawn on PAL pixel aspect screens. It's actually "320x200 used of 320x256 possible", so it's still a 320x256 resolution.
For NTSC/PAL monitors, you could resize the picture to perfection. You still can today, if you use a CRT!
Personally, I think that if you leave 1:1 pixel aspect you're in la-la land. Of course, if you have a good reason, such as only playing old "drawn for NTSC TVs" games and nothing else, or are setting up a display for a console such as NES where every single game was made with the "console resolution-on-TV" pixel aspect then it's vital.
And this leaves you with two choices, I guess. If you want to stick with 1:1 pixel aspect, you will have black on left and right border for PAL games, and black on top and bottom border if you play NTSC games. (Or borders all around, if you play "320x200-in-320x256-resolution" games.) There's no other way to display the whole picture and still have 1:1 pixel aspect.
Everything, not just Amiga, was made to be output on a 4:3-ish display until a few years ago. So the alternative solution is that if your display has a 4:3 mode, you can get pretty close to 1:1 pixel aspect for the vast majority of games, games that are made to support PAL.
It's easy to accomodate the 4:3 worldwide standard, if you have a proper display