Make the highest thing you can. If something uses 2 bars instead of one, that's double the xp you would get than if you made something that uses 1 bar.
I'm not sure the xp rates, but it goes like this
1 bar item = 10xp
2 bar item = 20xp
3 bar item = 30xp
and so on. So for speed, Just make the highest level thing you can that uses the most bars. I did mithril kites and plates to 70. If you want to save money, make arrowtips.