When choosing between the Offset or 35L Panniers, it comes down to a matter of preference in symmetry more than anything else and if you tend to overpack and want to limit this tendency.
If symmetry and having the bike look even on both sides are important, we recommend going with the Offset Kit.
However, you can always cinch down the 35L Pannier on the exhaust side to be smaller when not need space but then have the extra space when you need it.