What is the best lead when calling next on a declined bower?
I'm not a Eucre expert by any means, but in my opinion, not leading the ♡A is foolish advice. 

If that's the only heart in your hand, then the odds are greater that your opponents will also have hearts. As you say, the dealer is likely strong in red. The best chance you have of winning the trick is on the opening lead. Why would you lead a suit which relies on your partner having an ace or being void in diamonds?

The worst case scenario: they will have to trump your ace, and since you only have two trump, neither top, and one bower is turned down, it is good to force your opponents to use their trump in that situation rather than, say, using their trump to overtrump yours.

Secondly, and more importantly, after you lead the Ace you will be void in hearts, and able to trump any further heart tricks. You're already void in Spades and can trump any of those tricks your partner can't take. You can slough off your diamonds on spades or hearts if your partner takes those tricks.


  My general line of thought is that since I am void in spades, I'm best to become void in diamonds to increase my chances of using my trump on off suit leads by my opponents.


Why lead a suit that you have two cards in when you can void hearts immediately?