I've done both. As long as Fuego is still erupting, I would recommend the overnight. As you've probably noticed already, the prices vary considerably between companies (from $45 up to $125). The budget ones (easily booked through your hostel the day before) basically give you transportation, a Spanish speaking guide for the group (up to 20 people), some food, and tents/sleeping bags of variable condition. The highest priced ones (Old Time Outfitters and Ox Outfitters) are close to all inclusive. I went with the middle of the road. The company was NEWay tours.
https://www.facebook.com/NEWay.Tours/
They use local Spanish speaking guides from the village at the base of the volcano. At least one of the owners speaks fluent English. It isn't that big a deal if you don't speak Spanish because its likely that someone else in your group will.
No matter who you go with, be prepared:
- It gets cold at night. I went the beginning of February and it was -4 with a strong wind at the top. There was frost at the campsite (about 3/4 of the way up). When I did it as a day trip in August, it was still cold at the top due to the wind.
- If you come from sea level the altitude might get to you (almost 4,000 meters at the top)
- There are several experienced guides in La Soledad. The one I had, and the other guide with the same company that we shared a campsite with, were both good but I don't know how you would contact them ahead of time, other than through an Antigua agency. One advantage of using an agency is that you don't have to worry about transportation.
- If you choose the budget option, bring extra snacks.
- Most outfitters recommend about 4 liters of water - which you have to carry.
- Some of the higher priced options offer porters to carry your stuff. If you don't use that option make sure that you have a pack big enough to carry your stuff (water, clothes, etc) plus a sleeping bag, sleeping mat and possibly a tent or parts of one. I witnessed people carrying sleeping bags or tent parts in their hands as their packs weren't big enough.