I can't confirm this but I've heard Miss Kim is more floracious.

Personally I'm not a big fan of lilacs unless you have a dry location with full sun....they bloom for 2 weeks and thats all you get.

I have Syringa palibin and really enjoy it. it seems very fragrant and comparable to the vulgaris only not quite as strong. It's a good substitute. The shrub is much more attractive to me. It has a different leaf, smaller. It has a nice rounded shrubby form rather than a lanky, leggy heavy form. It doesn't sucker. It has some fall color which is nice. And I've had no problems with it and no mildew and very little care. And it blooms in less than full sun.

We have two Miss Kims and three S. palibin planted in the same bed in close proximity all. Full sun in the area all day. Planted there for about 15 years. We much prefer the S.palibin. Blooms profusely and earlier than the Miss Kims. Both spp. are good but prefer the S. palbin. Darker foliage and tighter habit. Blooms last longer (2 weeks or more) with S. palibin. Again, however, both are attractive minatures of the standard S. vulgaris.

You can find more differences and similarities between these two lilacs here - Miss Kim Lilac vs Dwarf Korean Lilac: Same Or Different?