I've got a pioneer head unit with USB, BlueTooth and 3.5mm in. I only use the 3.5 in. Haven't setup BT or USB yet. Probably does BT calling also, but I never use the talking part of my phone.
Agreed on the speakers. I have 6.5 Inifinity up front, 6x9 infinities in the rear doors, 10" kicker sub...