Panvel or Kalyan?

I will be arriving in the Mumbai area on a through train, and need to get into Mumbai (CSTM). I could get down at either Panvel (around noon) or Kalyan (around 1PM). I assume that Panvel is preferable, as the Harbour Line suburban trains to CSTM originate there, while most, if not all, Central Line suburban trains originate before Kalyan.

Is there some other consideration that I am missing?

I think Panvel would be a good option as you rightly mentioned that all the CST train start from Panvel. Be careful while boarding the train since a few trains leave for Thane also. There are indicators on the platform which will mention the destination station. CST will be CST and Thane will be T.

Remember to purchase the ticket before traveling.

Yes - Panvel will be better as you will also be able to reach CSTM earlier that way since you will be starting for CST early. The travel time from Panvel to CSTM is roughly around 1 hour 15 minutes. So assuming you get a train by 12.15, you should be in CSTM by 1.30. While if you go all the way up to Kalyan, you wont reach CSTM before 2.30.

As mentioned above, Panvel is a better option unless you arrive on a Sunday in which case the trains from panvel to CST do not run for most of the day. I think the service resumes in the evening, but it will be very crowded.

Many thanks to aarosh, neeraid, and danielsequeira. Excellent information, as always (especially watching for trains to the wrong location and the Sunday problem). It looks like we'll be arriving on a Friday or Saturday, so the Sunday consideration would not apply. For future reference, does the Sunday block apply to all Sundays, or just some of them?

Thanks again!

It all depends on where the maintenance work will be done during that Sunday. The blocks are usually between Kurla and Wadala or Kurla and Vashi or Vashi and Belapur on the harbor line.