I have a Kala acacia tenor, but I don't have a Mainland or Ohana tenor to compare it to. My tenor sounds great, though. I would say that it's a bit more mellow than my Big Island Honu traditional tenor, which is solid koa (both have aquila strings) but has a pleasant sound. Generally, I would think that because acacia trees belong to the same family as koa trees, solid koa soundboards and solid acacia soundboards would produce similar sound results. I think the differences in my Kala and Big Island tenors may be attributed mostly to manufacturer design and build.
Your question is difficult to answer though, because if you have multiple variables -- in this case both manufacturer and wood, as I don't think Mainland makes a solid acacia ukulele and I'm not sure Ohana does either -- it's hard to determine the cause of differences. An Ohana soprano may sound different from a Kala acacia soprano because of the wood, the design of the ukulele, the manufacturing process, or any combination. It may be best to triangulate. For example, compare a Kala solid acacia soprano to a Kala solid mango or solid mahogany soprano to get a feel for the differences in wood, and then compare the Kala solid mango to a Mainland and Ohana solid mango (if there is one) or compare a Kala solid mahogany to a Mainland or Ohana solid mahogany to factor out differences in wood.
Although sound samples can be unreliable because of variabless related to recording, it may also help to compare ukulele sound samples on YouTube. Good luck!