I received offer from both these universities. Please let me know which is better option and why? Thanks!!

This depends on your goals. Cranfield is the better business school, as reflected by the FT European Business Schools ranking. However, these are stronger schools for the MBA and PhD than for the MiM. If you were focused on finding UK employment, a better choice would be one of the schools in the FT Masters in Management ranking.

Take a look at: How to use LinkedIn to find the best school www.find-mba.com/board/33571 

If you are neutral between then, then I would pick Cranfield because of the higher quality of the students (e.g. GMAT, TOEFL), faculty (research, innovative teaching) and the fact that the university is focussed on graduate students. 

Hi Duncan! Thank you so much for your valuable insight.My goal is to switch from accounting to management consulting. (I’ve been working as an accountant for past 4 years.) BBS offers a strategy pathway which is why I applied & applied to Cranfield because it ranks high. Is there significant difference between these two universities? And also, does RG university give an edge?
Sincerely appreciate you for taking your time to clarify my query. :)

There are differences, obviously lots of differences. 

No, I don't think being in the Russell Group indicates much more than the scale and research orientation of the parent university.  It's less important than the alignment of the program with your goals.