I lean more toward the ultralight side of things so my instinct is 48. But, like @hikermor already said it is great to have the extra space if you need it. I bought my Gossamer Gear Mariposa 60 for that reason exactly. It is ultralight but also has a high load range in case I want to carry more than normal. I rarely carry enough to fill my pack but if you can compress everything well it shouldn't be an issue. DISCLAIMER: sometimes load range is overlooked when people are buying packs and just looking at capacity. A pack may have a 60 liter capacity but only be able to safely/comfortably carry 10-25 lb (like the Levity). Food for thought. Think about how much your gear weighs/will weigh as well as how much space it will consume. Good luck!

"I took a walk in the woods and came out taller than the trees."- Thoreau