Whatsapp is good (mostly) although the messages belong to the phone number, so if you change number you lose them and if you change phone with the same number it's very difficult to transfer them (in my case impossible
).
On the plus side it's "free" to sent texts, pictures even video other than a charge for the data if you don't have access to wifi, whereas if you used the normal texting app even on wifi the costs for MMS messages is astronomical, even a few emojis can end costing multiples of 25 pence.