I'm with 3 on sim-only with unlimited data and 4gb teething to be honest i don't know how much i use but i not watching videos all day or using music channel.
I do watch some 30sec or less videos when playing games so with updates i may be use 5-10gb a month.
The funny thing is i used my old Giffgaff sim the beginning of last week i paid £12 for mins text and 2gb data.
Only used it for the wife she was in hospital and our 3 network sim is a bit hit and miss there
so she used that for 2 days and used about 800mb so i still had well over a 1gb left.
a couple of days after she came out of hospital i used the sim indoors to play a game i was on it for about an hour all of a sudden i got a message from GG saying i had run out of data i couldn't believe it had just used over 1gb data.
So the moral of the story is that you can never have too much data Plus i think gg tucked me up LOL