I can help, as a longtime Hasselblad user who just bought a Mamiya 6 last weekend. I've had it a week now and shot 5 rolls of film in it.
I LOVE the Mamiya 6, and have put my Nikon equipment (Which I never use, I switched to Leica for 35mm work several yrs ago) up for sale to raise money to buy the other two Mamiya 6 lenses. I have the 75mm now.
What I like about the Mamiya 6: The lenses are INCREDIBLE. The 75mm Mamiya 6 lens is sharper than the Hasselblad Zeiss 80mm CF-Planar I have, and it is a VERY sharp lens. The camera is light and easy to handhold, and it fits in a little Artisan & Artist bag I use for my Leica. Hasselblad is too heavy for me to carry all the time, but the Mamiya has been with me everywhere since I bought it. I also like Rangefinders, and this is like a big Leica that takes sharper photos, and in 6x6 too! I like the square format a lot.
What I do not like: Close focus of 1 meter sucks. The Hassy focuses a little closer, and even the Leicas focus to .7 meter. The 150mm lens only focuses to 6 feet. I don't have the lens yet but I don't think I'll like that limitation. The camera's build quality is not up to Hasselblad standards. That's it, nothing else to hate!
I am not going to sell my Hasselblad; there are times I need its close focus, and I have extension tubes for it to get really close when needed. I also need longer lenses than 150 on occasion. It is not getting much use anymore though. My advice is that if you can live with the close focus limits and the fact that there are just 3 lenses, then sell the Hasselblad and get the Mamiya. If you can afford to buy the Mamiya without selling the Hasselblad, I'd keep the Hassy too. If you need other lenses or close focus and cannot afford the Mamiya without selling the Hassy, then keep the Hassy and forget the Mamiya. I think you'll like the Mamiya 6 though. I would not part with mine.
I shot these with it last week:
Both photos shot on Tri-X developed in PMK