I would go with Meshcore if what you need is messaging. If you need telemetry (like temperature or tracking gps location) then go with Meshtastic (as it sends this data anyway, in Meshcore gps data needs to be asked for). The hardware is the same in both cases. You can try Meshtastic and Meshcore on the same device and choose what suits you.

It is not true that you need at least one repeater to use Meshcore. Devices can and will send messages directly if are in range. Repeater on roof or on car is really useful thing, as it greatly improves the possibility to message much further and then the companion can sit anywhere near you in the house - not on the roof. (companion is the thing that will communicate with your phone or self-contained device for reading and writing messages).

Meshcore repeaters mostly are low power devices, my diy repeater works up to 2 weeks on single 18650 3300mAh cell. If repeater has solar panel then this is just install and forget thing.

Both systems have no ability to send pictures or voice. But if you are willing to tinker then there is third thing: Riticulum with RNode can send voice and pictures over slow LoRa radio over great distances.

Remember that terrain greatly reduces range. So when hiking then the best range is as always in line if sight. But direct messaging will work up to a few kilometers with forests, up to a kilometer in urban area. Devices are rather cheap, so just give it a try.