They are both good tires, I have had both. The biggest difference I have found is the side walls. Falkens have a much more tappered side wall giving it a narrower look. The Nitto 555 are very wide and blocky. If you have rubbing issues then go with Falken. My buddies 245 Nitto's look as wide as my 265 Falkens.
E90 335iA BLK/BLK 19" IForged Daytona, UR Intake, JB3 2.0, RR DP, AA intercooler, HKS BOV, KW C/O Street Comfort, 424whp