It's a pretty straightforward answer really: PCs like ISO files, and the Wii uses kind of its own WBFS format:
As wbfs isn't a native PC format the speed the data is being decrypted may/will causes issues (probably giving you the choppy run) - PCs can decrypt ISO files much quicker as it's a standard format. Dolphin can also read CISO & GCZ files: the first I wouldn't really bother with as it won't compress dummy files on a Wii disc, nor can it be read on a Wii, and gives you smaller compression than wbfs (but better speeds), GCZ on the other hand is the best of both worlds, but again is not supported on an actual Wii...
Your choice: if you've got the space (or can afford to buy more) the standard ISO format is the best. If you have a Wii as well, perhaps you're only playing certain games on Dolphin for that higher resolution? Just convert those odd games to ISO (using Wii Backup Manager)? If you're rarely playing on the Wii these days but want to save space, maybe look at GCZ (can use for both GC & Wii titles) - depends on how you're playing your Wii games these days really.
