Realize where your power is coming from and it makes sense to go to the battery directly. Anywhere else and you have to upgrade the wires going from the battery. Look at the size of the wire from your alternator to the battery. It is generally quite small in every car I have ever owned. Somewhere in the 10gauge area. It does not provide large bursts of power on a moments notice. That is the batteries job. The alternator is more of a constant battery charger than anything else. You do NOT want to run ANYTHING directly off the alternator without a battery present. There is a reason car manuals specifically state to never run the vehicle without the battery installed...
I know that people tell you to ground your battery to the Alternator bracket when you jump a dead battery but this is to keep the sparks away from your battery. A charging battery off gases hydrogen and if you mix hydrogen, oxygen and an ignition source things go boom... Like your battery. I have had a battery explode next to me and luckily I was wearing boots otherwise when the pieces hit my ankle it would not have been fun. I was a new employee and the equipment I was testing had not been run in a long time and the battery was bad. My partner was not aware they had abandoned the equipment so we were not supposed to run it.
So wherever you ground your system you want to make sure it has a good solid path back to the battery. Again this means upgrading all of the wiring from the battery to the place you are using your power.
In my area it is very common for people with large systems to ground their systems directly to their battery. But it can be expensive otherwise. I remember buying 1/0 high quality wire that was like $10 a foot or more. In my car I needed to run 15 feet of the wire so I ran both positive and ground to the battery. No worry about voltage drop there. The big difference between high quality wire and cheap stuff like welding wire is the size of the wire and the flexibility. The high quality stuff I had was about the size of OEM 4 gauge and was as flexible as a thick rope. Very easy to work with but the copper actually burned when I tried to solder it to a connector. (Had to use a propane torch because of the size of it.) Soldering 1/0 gauge wire is probably not the best solution. In that vehicle the 1/0 wire ran to a series of distribution blocks that fed the 3,000 watts of real power in that system. It was only rated at 500 watts but we used "cheater" amps. I used 2 Optima batteries and originally used a Diode Isolator but ended up with a Constant use Solenoid to charge these batteries. It was after losing 10 different chromed battery connectors to 4 different Optima batteries that I found out that Optima batteries are crap and not intended for use in daily driven vehicles and definitely not for car audio. One of my batteries was a factory replacement and the other was powering the system. One ground wire went to the negative grounding block and it was also grounded against the frame to ensure that the ground potential of the system battery was the same as that of the vehicle battery.
Sorry if I went a little off topic there.