<All of this ignores flavor concerns. If something doesn't feel right, pick something else.>
At first level, you should use a light crossbow to save money. By 2nd or third, picking a longbow makes sense. You are attacking with a +4 to do 1d8+2, whereas sacred flame would do 1d8 with dc 13 and a longsword would be +3 to hit and 1d8+1 (short sword +4 and 1d6+2). The 2 points extra damage trump SF's slightly better chances to fully connect (save DC vs. AC*).
At 5th level, switch to sacred flame. You are doing 2d8 now, and it has a better chance of connecting.
At 8th level, your bow damage increases to 2d8+2. Keep using that.
All of this advice changes if you increase your stats.
*comparing Dex save DCs to ACs for opponents is always going to be a rough estimate, since every DM throws differing opponents at you.