I wouldn't trust either company with any deal that didn't involve cutting me a cheque. I would trust salesforce not at all but at least with a cheque there is a chance they haven't completely screwed you over. With some kind of stock / options deal. Hell no.
Microsoft has a pretty good history of buyouts resulting in the bought out company pretty much being flushed, so again, regardless of the logic, I would not do a deal that I couldn't have go complete into the toilet and still have my walking away happy.
But if both companies made me the exact same deal, at least with MS I would trust the cheque cashing and not being somehow threatened with legal crap if I didn't give it back; if only to avoid reputational damage. With salesforce I would think, "OK, these MBA types now hold all the cards, being MBA types why wouldn't they screw me?"