Much depends on how you want to control your trains. If you’re just looking for round-and-round type of operation with little interaction, then track power is fine. Save your money on receivers and sound systems and buy another loco or three. You can even do basic operations–switching out a siding, etc. without any major fuss. I would recommend finding a power supply that allows you a wireless handheld remote to control your trains, but those are fairly easy to come by. (Older-generation Train Engineer trackside units come up fairly regularly on ebay, or Bridgewerks and I think a few others offer that option as well.)
Once you start wanting to add sound that you can control on command (i.e., not relying on track magnets to blow the whistle), then you’re looking at some kind of command control system, be it track or battery powered. You’ve just added anywhere from $100 - $350 to the cost of each locomotive you buy for a decoder or decoder and receiver, etc. You’re playing at a whole new level in terms of the work involved to install the sound and control electronics in your loco, but the control you get as a result is night and day different from turning a knob on a big power pack. As Pete mentioned above, you’re controlling the locomotive at that point; blowing the whistle, ringing the bell, applying the brakes with some systems to slow down and stop… it’s a brave new world, and you can experience it with either track or battery power.
I run battery power–I have for 30 years now. It’s a very low-maintenance approach to building a railroad. You lay your track where you want it to go and don’t worry about electrical conductivity or any of that stuff. The trade-off is that you’re limited by needing to make sure you’ve got charged batteries. Li-Ion technology over the past 5 years has made this much less of a concern than it ever has been previously. I can charge a pack and leave it on the shelf for a year, and it will still be mostly charged when I do finally plug it in to use it. That, and I’ll get 2 - 3 hours run time out of a pack the size of a deck of cards.
On the flip side, if you’re running trains that are power hogs (5+ amps per train), then you’re going to be swapping or charging batteries much more frequently, and track power is probably the better option for you.
It’s not an “either/or” thing. You can wire your railroad to handle both. Lots of folks do. That way you’re covered. I think once you equip a locomotive with battery power, you’ll never run it on track power again, but having track power available allows you to run others’ trains or to run your new acquisition while waiting for the battery stuff to arrive.
Later,
K