Dual battery preferrence: battery isolator or solenoid?

I am planing a future upgrade to the Taco, and wondering which has worked best for those of you that have done this. I plan to use a smaller sized deep cycle type for my aux inside the hood, just not sure if I want to go battery isolator (re-wire alternator to go to that), or use an isolating solenoid (up the gauge of the alternator wire to 4 AWG). I figure the aux battery will run any future add on lights, CB and winch, reducing further draw on the primary. I do plan on doing the alternator upgrade to the Caddy unit that seems to work.

 

The biggest differences are that a diode isolator is more reliable, no voltage spikes or current backflow, and more expensive.

 

Thanks. Sounds like that would be your choice, not considering cost?