I do both batch and fly sparging (mostly depends on the weather). I get usually about 89% efficiency with my fly sparging rig and ~85% batch sparging. If I was all about the numbers I'd fly sparge all the way, but I only like to do that when it's nice outside and I can sit around in the sun drinking some beers.
I fly. Always have for no real reason (initially) except that with my 3-tier keggle set-up, I thought it would be easier because the only thing I need to keep an eye on volume-wise is my boil volume. For sparge water, I can just fill up the HLT, heat it up to ~170 and sparge until I hit boil volume. This, coupled with the fact that I get 92% efficiency, will keep me fly-sparging. As for a complicated set-up, I don't think mine could be much easier. All I do is sprinkle the water coming out of the tubing from the HLT. Yes, it's labor-intensive, so to speak, when I could be doing other things for 45 minutes instead of sprinkling a hose of 170 degree water, but I don't think it's a big deal. I enjoy brewing and taking my time with it for now. But a sparge-arm contraption is on my mind.
I fly sparge because that was how I set my equipment up. I have a $5 PVC manifold in the bottom of the MLT and I have a $5 manifold that sits on top of the grain.
As a previous poster said, I over add water to my HLT by a gallon or so and then just watch my pre-boil target volume and stop when I get there. Last 2 brews have been right around 90%. Though I am more happy about 2 batches having similar efficiency than I am about the actual efficiency. I'm brewing tomorrow and I have adjusted my recipe for 85% this time.
I've never batch sparged, I suppose I should try but there just aren't as many gadgets involved!!!
I fly sparge, or, more correctly, I do the hybrid fly sparge discussed in BYO a bit back. (Adding 1/3 of my sparge water at a time, & draining it off at normal sparge rates) I recirculate during the mash, and I can maintain the clarity achieved this way. It takes longer, but is actually less work. I seem to enjoy it more as well.
I have only batch sparged. Mainly due to no fly setup and it's fast and easy to do.
But I am thinking of building a fly mainifold this weekend just so I can do it if I feel like it. Maybe on a day when I have a lot of extra time and some friends over to brew. It will give more time to relax and have a brew.
I fly sparge. The sparge arm I cobbled together at Lowe's from a large shower head, the type that mimics rainfall, and a barb fitting for the hose to attach. I just clamp it on my cooler MLT and adjust the flow rate. Cost less than $20 and it's easy.