In my opinion the most hassle free for a V6 would be a Terminator X Stealth system, or possibly the MSD Atomic II, but I don't normally recommend the EFI with the ECU built into the throttle body, like FITech, Sniper, etc.
I think swapping a LV3 in would be a huge upgrade, but I don't see how that wouldn't be a hassle dealing with the factory wiring and interconnects?
For a V8 I think the least hassle would be the Edelbrock PF4, because it includes everything but the fuel pump, regulator, and plumbing. It even includes a new distributor thats already locked out. Although I can piece that together from Holley and then you have more capability with true self learning.