I am not expert in IT development domain. But I would imagine product development is better option then maintenence of applications created by someone else. In my long stint with IT i have seen people are happier when they work for product companies as compare to maintenence (which aperently becomes routine). I somehow feel that product development experience will give you beter knowladge of product lifecycle which will be good for you in long term.
At the same time I want to stress that both SISL and accenture wont commit to keep you in a same project forever. In both cases it is more likely that you may be moved to totally different product / project.
Also between SISL and accenture it is obviously accenture which has more number of project with different verity. Accenture is known globally as compare to SISL.
so, this should be enough for you to decide.
At the end we can give you gyan, but YOU HAVE TO MAKE THIS DECISION

right ? Do let us know what you have decided.