let me see if i can help u make ur decision. i wud probably say Oxford for the following reasons:
1. You mentioned you are interested in entrepreneurship. Oxford (SBS) has one of the most entrepreneurial focussed MBA. The Skoll Foundation works out of SBS and is renowned for entrepreneurship in general and social entrepreneurship in particular
2. The Oxford experience is something which you can get only in Oxford (and Cambridge). No other university will give you the chance to rub shoulders with PhDs, scientists, inventors, literature students, archealogists, etc.
3. Oxford has many inventors and scientists with patents who do not necessarily have the business mind. It is a perfect mix for entrepreneurial MBAs. Come to oxford, study for the MBA, see if you can pick up some interesting invention, make a business out of it.
4. With regards to Kelley. People in USA may have heard of it, but no one outside would have. Now, if you consider Oxford, every tom, dick and harry in the world has heard about it.
5. Visa rules are something which always keep changing in every country. Some year, they are favourable, some year they are not.
6. Since you have 7 years of work experience, think hard about a 2 year MBA program. Will it give you value for money vis-a-vis a 1 year MBA?
I am probably being biased for Oxford, but that is because I have heard about Oxford and know about it. However, I have not heard about Kelley and hence won't know the other side of the story.
all the best