You are new so you couldn't be expected to know, but there was a HUGE firestorm about 2 years back, involving who has the rights to use the RAT name and designs between the 2 companies.
Ontario is continuing to make the knives w/ the original designs, there is much debate about whether 1) it is ethical for them to do so, and 2) whether they are making w/ the same materials and attention to detail (heat treat etc) as ESEE does.
One big thing about ESEE is their warranty, they stand behind their products to a degree that you don't see too often, I don't think the warranty is the same w/ Ontario.
As far as reputation in the industry goes you will find much respect for ESEE, whether all this means you are willing to pay however much more for their knife than Ontario's is another matter.
I own 1 ESEE, the Izula, and it's awesome, I own no no Ontarios so I can't compare quality firsthand.