Of the three you offered, because those are the rules of the game, I'd select the Walther. Why?
1) I've owned a P220 and I'd never actually carry it because of it's size. As attractive as 45ACP is, I wouldn't select such a large gun especially having an 8+1 limit. 8+1 itself doesn't bother me at all--I carry a Kahr K40 and have no concerns about its 6+1 limit. I just wouldn't choose something I consider enormous AND pay an unnecessary penalty in capacity. In my experience shooting 45 as fast as possible, I can do quite a bit better with lighter, smaller 45s. I find it a little cumbersome, although I must say that, in shooting IDPA with it, the SA/SA trigger was never a factor and never really noticed. I've never found trigger weight, reset length, or anything else to be a factor when I've shot all stressed out--it's not there.
2) The Walther is available in 40SW which is my preferred 'lightweight' round (the lightest I'm comfortable carrying), it appears to be a fairly 'right-sized' gun to me, and justified considering the 40SW and capacity options. With what appears to be virtually equivalent to a SA trigger, it would be my choice--but I've never fired one and of course would want to at least handle and dry fire one if that was the only 'pre-flight' option.
3) P250sc appears to me to be a very small DAO, with impressive capacity, but my experience in learning to shoot a small DAO pistol has been a real challenge. I'd expect it to be an excellent pistol that most folks would tend to carry regularly because of it's size. Being available in a 10+1 40SW configuration is a big plus to me--but I expect it take extensive practice and patience. Not a bad thing, just my 2nd choice as I've already done it and it requires a lot of attention. A somewhat larger handgun is, to me, an advantage regardless of trigger. I'm not familiar with any of Sig's polymer, striker-fired weapons, and if interested in this gun for some reason, would want to at least handle and dry-fire one. Just because a manufacturer advertises a product as 'DAO' doesn't mean it's DA in any familiar sense. I think S&W still advertises their M&P line as 'DA' or 'DAO', and the 2 I own are as SA as any gun can be.