I love my DOS 6.22
I took my copy of Windows 98SE and peeled the MS-DOS 7.1 from it. Makes a dandy VM (virtual machine) under VMware or VirtualBox. Runs faster than you can imagine.
The advantage of 7.1 over 6.x is the support for the FAT32 filesystem so you can have more and bigger files, long filenames, larger disk volumes, and compatibility with Win95 and later if that's a factor in your use case.
The only tricky part is that since Microsoft didn't release MS-DOS 7 as a standalone product, you have to get Win98 and ignore the Windows part. Fortunately, I had copies of Win98 anyway, so no extra cost for DOS.