You are comparing apples to oranges... First figure out whether you want speed, steam, or combi steam. I think that most people are served better by combi steam rather than steam only just because they're so much more flexible. Then, look at brands. I know nothing about Miele or Wolf steam ovens, but many people here own them so they will probably share their experiences. I do know though that Gagg is the best of those, because you can get it in a plumbed version, you can control the humidity (not just steam on/off) and it has some other nifty features like the ability to condense the steam before you open the oven so you don't get a blast in your face, and a button to add bursts of steam manually during cooking. If you decide on a Gagg, look for floor models or Ebay/Craigslist deals to help alleviate the sticker shock. There are tons of deals to be found on those ovens.

As for functioning as a microwave, the steam ovens will not replace a microwave exactly but they may take over many of your microwave's duties. They are excellent for reheating things, and although they take longer than a microwave, the results are much better. The Advantium, as well as most speed ovens, can function as a microwave alone. If you only use the microwave occasionally like me to heat up things, a speed oven alone would be fine. However if you use the microwave frequently you should probably get another microwave to supplement the speed oven for two reasons. One, while you are using the oven to cook the microwave will be out of service. Two, to preserve the life of the magnetron.

Thank you so much, very helpful hctech42