Moissanite is a gemstone made of silcon carbide, whereas Asha is a CZ diamond simulant; therefore, moissanite is its own stand alone gem and Asha isn’t. Asha is harder than most CZ’s because it has a diamond coating, but it still isn’t as hard as moissanite. I believe moissanite is a 9.25? compared to a diamond being a 10 on the Maid/Matron of Honor scale. Betterthandiamond.com and moissaniteco.com both have great education pages for moissanite (I think moissaniteco’s is more helpful). BTD.com also has information on Asha.
Amora can mean two things (confusing, I know). Right now, the only Amora that is available is a treatment for moissanite that makes it show less color. In the future, (the estimate is 2015 for the US) there will be an Amora gem for sale that is an entirely different silcon carbide gem. According to all the info (available at BTD.com) it will kick moissanite and Asha’s butt, but it isn’t available for years.
If you want a D-F color stone you would have to go with Asha. Even enhanced (Amora) moissanite only comes rated as high as “H”, and it will be rated as an “I” for 2.5ct and larger stones. However, you may be surprised at how much you like it anyway. I considered myself very color sensitive, but I loved the loose 3ct Amora moissanite I ordered that was rated as “I”. I am in the process of having it set, and they are supposed to show even less color when set than when they are loose.
All Amora enhanced moissanites are chosen because they have an excellent cut. I don’t know about Asha, but I haven’t heard negative things about their cut (except for the step cuts like emerald). OEC is an old european cut, which is an antique cut. It is available in both Asha and moissanite, but it is hard to find Amora enhanced OEC moissanites sometimes because they sell quickly. However, if you are worried about color, you should know that OEC’s show more color. I’ve heard they are more J-K according to size rather than H-I, but I can’t personally vouch for that. The RB cut is different in moissanite (Amora or not) than the RB cut for diamonds. Some people claim to be able to tell the difference with a naked eye. Maybe they can, but I certainly can’t and neither could my jeweler. From what I’ve heard, the OEC cut is the same either way. All Asha cuts are the same as diamond cuts from what I know.
I considered all three of these stones as well. I decided against Asha because I am rough on jewelry, and I was afraid it would hold up. I decided against the Amora (not moissanite) gem for the time being because it is not available for several more years, but I may upgrade later if I’m not over the moon with my moissanite. I chose moissanite and had it Amora enhanced because it was important to me that it was as colorless as possible, which is why I chose the RB over the OEC cut. I would definitely recommend Amora enhanced moissanite, particularly in the size stone you are considering.
I don’t know if you want to pass the stone as a diamond, but I chose to so it was important to me that it was not “off” looking. I can’t tell the difference when compared beside a diamond of similar size and color (2.5-3ct;H-J color range) and neither could my jeweler. We mixed them up to be sure, and he had to measure them to ensure we weren’t wrong about which was which.
Sorry for any typos, I should be getting ready for work so I was in a rush. I hope this helps!