Thanks for all the replies.

Like some have stated above, Amtrak is the only rail option between Baltimore and Philadelphia. I'm mainly interested in commuting between the area around the PHL station (30th street) and the BAL station (downtown Baltimore) so buses are also out as far as I can tell.

From what I've read and seen in the replies, it seems there are two options that would provide trips for the lowest price:

1) Multi-Ride tickets. Main drawback being the list of restricted trains on Northeast Regional (primarily around rush hour/weekends) which are not eligible for Multi-Ride.

2) Purchase well in advance of anticipated dates and refund as needed. Not as convenient as Multi-Ride but not restricted around rush hour/weekends.

Given that many of my trips will probably fall on those restricted trains based on my schedule, I'm probably better off just purchasing tickets for every weekend a few weeks to a month in advance and then just refunding the trips I don't end up needing.

Do folks agree that this is the best option given the circumstances?

In either case, I'll sign up for AGR to credit my trips.

Thanks for all your help and any additional comments!