Which miners to invest in?

Hello, everyone

We’re planning to invest a few hundred thousand dollars in mining. We have a network in China that can help us secure reasonable prices for both new and used machines, plus more than one facility giving us excellent prices for hosting.

We are not sure what machines to look for. As for now, the E9 and A11 look very far from being released. We were thinking brand new L7 (I believe 17/18k) or used M20S ($4500).
I would appreciate some advice from a much-experienced community like this one.

Thank you very much,