1. Animal is fastest and the rules stay the same and will last for years. Very little maintenance.
2. Clones are next in speed and will not last as long as the animal and requires more maintenance, rules change often requiring new parts.
3. Lo206 is close in speed to the clone. Will last forever with very little maintence. There are no rule changes in this class, Cheapest engine to operate out there.
4. Flathead is losing popularity and requires more rebuilds than any other engine. Some say it is the slowest unless built into a limited class.
Clones are ran by more people (in some areas) because that is where the payout are. Builders and part suppliers and importers make more money off the clone than all the others combined. So they put the money into the money races. It is one of those (follow the money trails).
I still run the animal and am very happy with it. Not as much money in the races, but I really like not having to keep spending a fortune chasing the latest greatest part of the week clone club. Owned 3 clones, been there done that, did not like it. Went back to the original animal that is now 7 years old and love it. not into Lo206 because I like to go faster than they go. Probably a great engine for beginners and kids . That is one drawback of clones, they are not fast like the animal.