I went down this road when I worked for Siemens years ago. The main difference (beside there not being an "Automatic" version of UL98) is in the overload, opening capability and endurance testing.
UL98 overload capacity is required to be 150% of rating for 50 cycles (about 8.4 seconds) where the PF is greater than .75. So if the load is all motors, it isn't going to qualify without being seriously over sized. UL1008 requires the 50cycle overload rating to be 600% at a .4PF, i.e. good for 100% motor loads.
UL98 contacts must open a load at 600% of it's rating 3 times. UL1008 must open 1000% of rated current under similar circumstances.
UL98 is tested for a specific number of operations that varies with size. UL1008 requires more test cycles in most sizes, equal to UL98 in the rest.
In addition, there are temperature and Short Circuit testing requirements that, although similar for both, have one important little difference. With UL1008, the same unit tested for the above issues is used in the temperature and SC listing. With UL98 they are allowed to substitute the unit after each test with a fresh one.
Still, I'd say that if you are looking at residential / light commercial units where manual transfer is all you need and the load / duty is not extreme, a UL98 DPDT Safety Switch is fine. Anyplace where standby power is REQUIRED but can be manual, a UL1008 listed switch is going to be necessary.
