Dear Choices 4 Grad Studies:
Both the MBA and graduate studies in computer science are "high opportunity" areas for current market conditions.
Having an undergraduate degree in architecture is not an impediment to either path. The MBA is independent of the specialization in your first degree. In the US and Canada, you can pursue an MS in computer science. It typically requires a 4-year college/university education in any discipline, insofar as the academic requirements are concerned.
You are obviously interested in the "bang for the buck" for the degree you pursue next. We would note that the financial return on an MBA degree is highly dependent on the quality and prestige of the academic institution, much more so than the return on a computer science degree.