Ah, the 64 million dollars question… Well, when all said and done, that's about how much it would cost you. ;-)
The answer is depends. It's like you have outgrown your VW bug, which is a better car, a Volvo Outback or a Ford F350? Again, depends. What are your cargo and how much money you want to spend?
The only thing you can move is the data. Even that, I would hesitate to move directly into either database. More about that later.
What hardware and software do you have? What hardware/software are available for use with the new database? Do you have the human resources, such as DBA, programmers/developers? How much time do you have to implement it? What do you want the database to do for you? How about the politics in your company? Pro-/Anti- Microsoft/Oracle. Regardless which one you choose, it will not be cheap. Last but not least, do you want to contribute to Bill Gate's $40+ million still-in-progress-beta-901.14-build-4087 mansion or Larry's $20 million sailboat? Unfortunately, there many questions/issues you much address first.
Back to the data. Getting the data into SQL or Oracle is relatively easy compare to others issues. I would redesign application to take advantage the strength of the new database. Also, a good chance to create an application that works well with the database and any future needs.
I would recommend reading the white papers on Microsoft and Oracle web sites. Also visit other site like this one to learn more about the strengths and weaknesses of each product and see if they are something you can live with.
Sorry, no quick and easy answer. Since no 2 companies are alike, you will have to do some homework and figure which one is more appropriate for your company.
Remember this, if you don't have the resources to do it right the first time, you are not going to have the resources to redo it later.