There are lots of reviews on the mimi and other similar products. I'd check all of them out.
It's seems like a pretty straight forward waterproof clit vibe, and I'm pretty sure it's one of the less expensive "luxury" ones. The nicest non-waterproof version out there is probably the Siri by Lelo. JJ makes three waterproof vibes that you could compare it to as well, the form 2, form 3 and form 4. The form 4 can also be inserted as well as used on the clit. Pretty sure all of the JJ's are more expensive though.
As for the Mimi, i haven't tried it for myself. I've heard mixed reviews on exactly how strong the vibration is. Naturally different people consider different things "super strong." If your ideal is level "high" on the hitachi, then your opinion of what's "way too weak" will be very different than someone who thinks the Gigi is as much oomph as you'd ever want or need.
I'd look for reviews that talk about that specifically, and see if you can't find people who are familiar with the toys you have used and like to see if the Mimi offers what you're looking for.
mine just came in last week. i love it. iv used it like 4 times on the first charge plus jus having it on & playing w. it alot. its absolutely lovely & soo silky soft. it is an entirely well built toy in my opinion but some peoples have malfunctioned. i read many reviews & compared it to many different toy & bought it in spite of the chance of it going bad. it has a kinda rumbly vibration that goes though the entire body of it.some people have complained it makes their hands numb but it wasnt a problem for me. i think shes all around pretty awesome & so far im very happy w. my purchase
MiMi is by far my most used and most love toy in my collection.
As Cherrylane said, if Hitachi on high is the only thing that will get you there, MiMi might not work. Otherwise, she's pretty darn strong. I need stronger vibrators (MiMi, Form 2, Salsa) and MiMi is my go to. The silicone is smooth, it's waterproof, the charge seems to last forever, and it fits in the palm of your hand. Oh, and the vibrations are more rumbly than other clit vibes.
The buttons are a little hard to press, but that's the only downside I can find.
I don't think anything can be called the "best", but a lot of people like the Mimi. Read reviews, and see if what people say about it appeal to you. It's pretty much up to you if you feel good with it.
I can't say it's the best, because I haven't tried EVERYTHING. However, I've recently been trying tons of luxury clit vibrators and the MiMi is still my gal. I've used it during EVERY session since the day I brought her home and I even replaced her when my dog ate her! I love it that much. You have to love a toy that much to actually pay full price to replace it.