One thing I have come to appreciate about WhatsApp is its ability to handle low bandwidth environments better than iMessage. Back in 2015, I was traveling around Europe and had T-Mobile's unlimited roaming plan. I think the data speed was capped at like 64 or 128kbps? In addition, many hostels had less than 1Mbps wifi. iMessage would just choke trying to send pictures or large messages. In particular, it would be stuck in the middle of that "sending" blue line indefinitely like it was quietly timing out and would sometimes require a reboot of the phone to recover because it would remain stuck in the "sending" phase forever. Whatsapp seemed better tested and more solid when it came to transmitting messages. You'd see consistent progressing updates in the progress bar until it either timed out(unlikely) or finally transmitted.