I differ from fly girl...
If you are an EXPERIENCED Helicopter pilot for SRH or multi,than manual mode is the best for immediate judgement. I will be flying my first Hexacopter in manual mode first. Since if GPS/compass is not set up properly than I may have a fly away or issues with it on the maiden flight.
Now if you are good at flying Rc Heli's than use manual as you are in control. If you are not secure within your own skill level than use Attitude mode, that way if you are anything else failes you can simply cut throttle (Dont fly above 10 feet for maiden, personal rule its up to you)
I usually fly my Multirotors in Attitude mode since im focusing on camera, but on maiden low height flight or indoors its manual. But please please please do not listen to me unless you are very confident in your ability to control the craft in this mode. I have crashed and im sure everyone else has too, f450 can cause a lot of damage to your wallet and others around you. Over everything else, best of luck! and have fun!