Will low water use toilets clog more?
Some of the low volume toilets manage to flush very quickly because of newer designs. Some of it has to do with coatings on the bowl, and the pathways inside of the toilet. But one change that makes a large difference is a larger flapper and opening that allows the water to drain much faster (the only downside is that you'll need special replacement parts in the future).

The last time I was shopping for toilets, they had a rating of how powerful the flush was in each toilet, which is much more useful than the gallons per flush. My newest toilet flushes much better than any of the older toilets, while using much less water.