Dear Vishal,
Both are Good companies..
When it comes to Seniors & Managers, there are Good and Idiotic kind of people everywhere...
Few people would have got good experiences and few would have got bad experiences in the same company.
Career Growth will be there in both companies, however bench depends on your luck.
To my knowledge Bristlecone has may projects of SAP Labs bangalore.... When it comes to Brand name i think Capgemini is little more than Bristlecone....But you should note Bristlecone is also a branded company.
In short, both are good...you can see for other factors to decide like if the offers are in different cities, go for the one which is nearer to ur home or parents.....
All the Best.
Regards
Shaik