See both of the exam is not a T-20 but its like a Marathon. So you should be passionate about what you are doing. If you are interested in MPSC go for it, if you want to go for CA just go for it. The success rate we always consider is always dependent on a sample size but not on a quanta. So you have to explore what creates more probability for you rather than that of a sample size. But if we consider a matter of fact then cracking CA in > 2 attempts is maximum where as for MPSC getting selected in 2/3rd attempt is quite often. So CA can be said to be a bit less probabilistic than MPSC but I would say you should explore your own potentials and find out what will be the best choice for you.

To know more about CA visit the link below:

https://www.careers360.com/careers/chartered-accountant

To know more about MPSC visit the link below:

https://competition.careers360.com/articles/mpsc-syllabus

I hope this answer helps. All the very best for your future endeavors!