You should always let your wines finish to dry.
Almost every new winemaker has a little trouble trying to get a handle on backsweetening. Here's how we approached it- We'd sweeten the wine to our liking, then take a hydrometer test and make a note of how much sugar it took to get to that SG. Next time we bottled, all we had to do was look at our notes.
You'll end up using different SG's depending on the wines you make. Whites, which typically have a lower PH. may need a touch more sugar to balance out the acid. On wines that have delicate flavors, you'll want to be careful with how much sugar you use in order not to tamp down the flavor.
Once you have the sugar amounts written down for all the wines you make, you'll just refer to your notes and not have to take SG readings every time you bottle.
As a side note, you should always take PH readings and adjust your acids pre-ferment so that your wines are nicely balanced and you're not trying to use sugar to mask high acidity. High acidity is a wine fault due to lack of adjustment and sugar can't balance out acids that are way out of line.