which VW engine coversion seems most reliable?

Looking at the various conversions, such as Limbach, Hapi, Revmaster,
Great Plains, and I'm sure there are some others, I'm wondering if one
or the other has a reputation of being the best for reliablity?
The Rotax seems based on the VW, although the company denies that,
just looking at some of their models, the resemblence is too much not
to be somewhat a derivative of the VW. Looking around on the web, the
Revmaster seems to be the only one with a stand alone engine for sale,
Great Plains seems to sell the parts to make the conversion, and
Limbach and Hapi I can't find any parts for them for sale. If they are
even in business any longer.
Rich