I was kind of curious about this so I did a little looking into it.
I'll do Iron last because I'm unsure of some things on this server so there's a couple cases.
The numbers listed are going to be xp earned in smithing per one xp earned in mining.
runite: .24
adamantite: .25
mithril: .29
steel: .41
I was reading through another guide and it said that you get 1% more chance to successfully smelt iron ore per level up to level 45 which would end up giving you 80%. I'm not sure if this is how it works on this server. Also there is the ring of forging? The ruby ring that gives 100% smelt for 140 ore. so given these scenarios.
100%: 1.07
80%: .85
50%: .54
You also have to take into account the time it takes to mine / smelt each of the types. It might take more time to mine the coal for higher ore, but it will also decrease the time you will spend smelting / smithing. There is also the question of profit.
So if your only goal is to level mining and smithing evenly I would say stick with iron, but for quickly leveling, other methods may be better, as well as for making a profit.