SE's are usually a good choice to get when a person is looking for a non pda-, or smart phone because of they offer alot of features. But it just comes down to you. The Dash is a Windows Mobile phone. If you are going to be one of those people who want to sync it with you PC and push Outlook, along with being able to download and install 3rd party software, then you should get the Dash. But, if you honestly do not need the capabilities that a smart phone has to offer and are more concerned about the looks flexibilty of the phone, then I'd just buy the K790a. The K790a's UI is good enough for any business consumer to get by. Of course, if you're thinking about watching videos on your phone, you'd have to convert them to Quicktime 3GP on the K790a. On the Dash, WMP will play straight up. However, I've never been privy to WMP because the audio does sound a bit tinny.
Not one phone is perfect, so there are still quirks that each one has. The Dash, like you already know, is a Windows phone. It's probably going to be prone to its random "crashes" once in a while. However, just do the usual power cycle, and there shouldn't really be a problem. SE's, on a few occurences, have the random White Screen if something is done improperly. With that, just update the firmware.
So basically, if you're thinking about using your future phone for multimedia purposes, go for the K790a.
