.... which one you would like to choose if u only have the choice between BTC and IOTA?
Well if you have a big amount like $10k then instead of putting it all in one basket why not split it between whatever options you have got.
What matter is the split percentage. I would split it into 4:1 ratio where 4 would obviously be for BTC.
Bitcoin should always be the first preference if the amount you are gonna invest is greater than $1000.