3-2-1 an 2-2-1 are very nice guidelines. Good place ta start. However, I do spares an it does sorta depend on the rib but, I've trimmed it down ta 3 in smoke, 1 wrapped, an 1/2 unwrapped ta dry em up a bit or 3-1-1/2. The 1 I put the ribs in a roaster pan in the oven covered an then fer the 1/2 I put em on a cookie sheet ta dry em in the oven. Use the same 225* heat in the oven I did in the smoker.
Ya can sure do the whole thin in the smoker, but usin the oven is quick, easy an saves some aluminum foil!
The idear is they er done when the meat pulls back from the bone a bit an ya pick em up with tongs an they bend nicely without fallen appart. This will give ya a rib with just a bit a "bite" to it without bein tough an yet won't fall apart on ya either.
Make sure ya pull the silver membrane on the back to.