Wow... this is a tough question to answer. A really good question though.
I would probably be more likely to purchase a Nokia with an OS other than Symbian. Symbian's health appears to be better but I'm not willing to take another gamble until they can get the management in place to properly develop and manage that OS on their devices. Nokia makes great hardware for the most part. So if they go with another OS, I would be willing to give it a look.
With that said, WP7 and Android are so different (and I've used both pretty extensively). Android is more than capable in doing most tasks. But it's achilles is the same weakness that Nokia has. Updates depend on the phone manufacturer. And nothing against Android, but the UI isn't anything great. It's very symbian-ish but simplified immensely. Nothing groundbreaking. WP7 is built on the windows mobile platform so it doesn't appear to rely on some java backbone. But it's such a new OS that it's missing a lot of basic features. But what it does do, it does great. The strength that WP7 has is that updates are done my Microsoft and not Nokia.
If they decide to do Android, it'll be the death of Symbian. They have a hard enough time with one OS that having a team just to keep Android updated on future phones would be too much. If they decide to do something for the short term, then WP7 would probably require the least manpower now and in the future until they can get Meego released and mature.
