I prefer soiless container mixes because they're lighter in weight (*see: back problems

*). IMO they also drain better and, therefore, less chance of suffocating plant roots. However, I only use a pre-bagged mix (Pro-Mix) very sparingly when I can't make my own. But I still add some compost even to the pre-mixed stuff. When I make my own, it's peat moss, vermiculite, perlite, some lime, kelp meal and compost along w/a small amount of some granular fertilizer. (The amount depends on the size of the container.) I used to use Safe-n-Simple organic fert (5-5-5). Then I tried Espoma's Organic Planttone and Flowertone for awhile. Most recently I've been using an organic granular fert from
Alaska brand.
I don't add any fert right away. Give the plants a chance to acclimate to the soil and transplanting first. Plus, they've just come from a nursery which has no doubt added fertilizer and, most likely, that timed-release stuff. (Ever see those little mushy-yellowy egg-like things in the soil? That's the timed-release fert.) So, I'll sprinkle some of my own chosen fert on the surface the next time I have to water them and fork it in.
After that it's foliar feed every few weeks or so and water-soluable fert added to the water for a drench every third or fourth time they're watered thoroughly. ONLY, when the fert's in the water, I don't water till run off, as you'd usually do when you water containers or baskets. Hopefully, that keeps the liquid fert contained in the pot long enough for the plants to take it up.
Just a few weeks ago, I lucked into a water-soluble fert that I'd seen advertised in OG magazine. OMRI approved, called
Multi-Bloom. This will save me a lot of heavy lifting of watering cans!

BTW: I got it - of all places - at Lowes!