I always make the Bookkeeper, Broker, and Manager the same dwarf, and it's always worked reasonably well.
I generally do the same, and then toss on something like engraving or stonecrafting for when they aren't busy with anything else. Actually, those are good matches for any noble slot. Rarely is engraving or stonecrafting needed immediately, and it is generally easy to have a second one for times when you absolutely need to have that fortification carved out right now.
Make sure to avoid time sensitive or intermediate tasks. A noble butcher for example is a terrible idea because butchers need to get to work ASAP to prevent kills going to waste. Tanners are bad for the same reason. It's also a good idea to avoid things like thresher, furnace operator, wood burner, weaver, etc. because having a stall on producing thread can screw up an entire industry.
You could also go for something like weaponsmith as you aren't likely to be making tons and tons of weapons, however that can occasionally be time sensitive when a siege is on the way. If weapons are going to be a big export for you though, you'll want to reconsider.
So, to sum it up: Stone/wood/bonecrafting and engraving are great and avoid time sensitive/intermediate jobs.