It depends. Your company does not necessarily have to be PROFITABLE (although if it is that will be a differentiator for sure - most start ups fail, and most are not profitable. If yours is, that will get the adcom's attention for sure), but ideally it will at least have a track record of success/impact. What matters most though is your role & the impact YOU'VE had at the company. When you've started your own company most likely the adcom will not have heard of it (if they had you probably wouldn't need the MBA), which means you need to PROVE to them that the work you've done is significant & meaningful & has given you a strong foundation in business that will allow you to uniquely contribute to their school. It's not that hard/unique to start a company. (As you know, most of them fail). It is unique to start a successful company & to have had big impact via that company. In other words, there's a huge difference between having stared a company that has 5 customers and a few thousand dollars in revenue vs. a company that has hundreds of customers or $1MM+ in revenue. The more impact you can show that you've had via your company the better. If your company is small or has not had much impact that's not to say there's no way you'll get into a top school - you'll still have gained valuable skills - but you'll need to be sure to show the impact you HAVE had in other parts of your career since ultimately the adcom does want to see results. Time is an important factor as well here - ideally you've got at least 2 years of experience at this company so that you've had time to show meaningful results. They won't be impressed just with the act of starting something. They want to see what you've accomplished there.
To answer your question, it's not inherently better to have worked at a place like Microsoft. Yes, Microsoft is a known company with a good reputation so that helps, but again, what matters is the impact you've had and the career progression you've shown. So if you've driven meaningful quantifiable results at Microsoft and have a promotion or two under your belt in the span of say 3-4 years, awesome. Ideally they want to see you driving increases in revenue, leading initiatives that reduced costs, managing teams, etc. If you've worked at the same job in Microsoft for 3 years and have little to show for it in terms of results then it's going to be tough to get into a top school. The brand name isn't going to save you.
Let me know if that answers your questions!