Did both, found I much perfer the cooler MLT.
BIAB was convienent for the sake of one pot, but it was more work dealing with the hot wort/spotty volumes/etc.
My 5gal cooler was $16, dual lined 5gal paint strainer bags was $3, and I use the spiggot that came with the cooler to drain it. Now I always hit my boil volume, and clean up's about the same with just a cooler to wash out in the tub.
Much happier with the cooler. YMMV.
Primary 1: Fauxtober Festbier
Primary 2: Open
Primary 3: Mistress Maggie (Irish Red)
Bottled: GB1, ESB, VNB, BBD, AZB, OOA
On Deck: Lith Keptinis, All Other Brews Subject to Change With No Reason - loving small batch brewing!