I'm on about my 8th gallon. I'm using 1 gallon carboys & trying a different recipe each time. I like a slightly sweet cider, more like a Woodchuck brand cider than a Crispin or an Angry Orchard brand. So I tried adding sugar thinking it would make it sweeter. Wrong. It just took longer to ferment, then came out with higher alcohol content. My first batch, fermented right in the half-gallon jugs it came in from the store, I used a baker's yeast and added no sugar. It was ok, drinkable, but very dry.
Then I tried a champagne yeast. It tolerates up to 19%, and no matter how much sugar I added, it was still dry tasting, until I topped out at SG of 1.15, which was almost like syrup. Final ABV was over 18%, but there was still some sugar left. Too strong. I tried adding white cane sugar, and also adding thawed frozen concentrate apple juice to reconstituted juice until I got the SG above 1.1. It makes for some very strong cider. Apple wine, really. Not exactly what I was going for.
I've always used store brand or inexpensive apple cider to start.
The last few batches, I bought a small bag of toasted oak cubes from a local brewing store, and added a dozen cubes to each gallon carboy, right at the beginning. Gives a mild flavor and good aftertaste. Very pleasant.
I've also tried adding spices when I rack it out of the carboy into the plastic jugs it came in. 1 clove per half gallon, a pinch of freshly ground nutmeg. I leave it in the plastic jugs until my supply of empty bottles is ready, then bottle it & it sits another couple weeks. Spices give a good complex taste.
Recently I switched to an ale yeast on the advice of the guy in the brewing store. They were brewing a 6 gallon pail of apple cider when I went. They used the local store brand of apple juice, a whole small bag of oak cubes, and the ale yeast he sold me. No sugar added. He said it takes about a week to ferment. I'm trying a batch now, but won't get to the drinking stage until 3 or 4 weeks from now.
Right now I'm drinking from a batch that started with a gallon of store brand apple juice, 3 cups of sugar, and the champagne yeast. It's 13% ABV, medium dry and has got a good color.