Well, the only preference we have--and it's only a slight preference--would be for a FFM triad. My wife is bi and we'd like to share a girlfriend. That said, I think that's less likely than other arrangements.
We had a FMF V for a good while, as I had a girlfriend. That ended last autumn. The wife is looking primarily for a girlfriend, so that would make for a FFM V. If we both end up with partners, it'll likely be a FFMF kind of thing--and I'd probably die from estrogen poisoning or something!
I suspect we'll stay with smallish groupings, as I can't see a large network being as comfortable. However, I've no experience with a large network, so I could be entirely mistaken. From where I am, it doesn't appear to offer the intimacy of a small group, though I can theoretically see how a small part of a large group can provide the intimacy while the larger network expands on it with greater variety.