I brewed Jamil's dark English mild last spring, and bottle conditioned a 6 pack with whole foods cola and with Virgil's root beer (3 bottles for each soda). I used ~10 mL of soda per 12 oz bottle, which gave me somewhere around 1-1.2 vols of CO2 (in addition to what was still in the beer after primary). I probably would go higher next time, like around 15-20 or so mL's per bottle for a better carbonation level. The cola stood out a lot; much more than I expected. The root beer mostly added a cinnamon and spicy note. I probably liked the root beer better. The cola version just tasted like someone put cola in my beer, and a lot of it, lol. I used whole foods cola because they were out of Virgil's Cola, and because it uses cane sugar and real kola extract. If I were you, I'd just do the same thing I did and bottle condition with whatever soda(s) you want to try, and possibly vary the level of soda/carbonation in some of the bottles. 10-15 mL in a 12 oz (355 mL) bottle has more impact than you would think. Most sodas list the amount of carbohydrates or sugars on the side of the can, so you can get an exact measure of how much you add. They're also sterile, so you don't have to tool around with boiling them.