I've always fly sparged. No particular reason, other than that's how I've always done it.
I think it really depends on your setup; I like fly sparging as I have a 2 tier, gravity fed system and I can set the HLT and MLT flow to about 1 litre per minute and just let it go. I usually dial my recipe in for a slightly lower than measured efficiency so I can just let it run until I've collected the required volume without worrying too much about tannin extraction.
I've also experimented with no-sparge, but found it's too inefficient.