Hearthstone strategy problem, kill with hero ability or minion, secret involved?

I ran into a typical Hearthstone strategy problem which is quite common, whether to kill an enemy minion with hero ability or my own unit. The problem is especially tricky because the enemy has a secret. Here is the situation:

So, here we have the situation:

Board:
   Mage vs Mage, 3 mana
   White has 1-3 (Mana Wyrm, +1 to damage on spell use)
   Black has 2-1, 4-3 and a Secret
White's hand:
   Coin
   2-2-2 Kobold Geomancer (spell buff)
   3-1-4 Dalaran Mage (spell buff)
   4-3-6 Water Elemental (tank)
   6-6-6 Phoros (legendary)
   4---- Cone of Cold (freezes + damage)
   4---- Polymorph (removal)

I am playing White, what should I do? At the time I considered that I had two options:

1. Use Coin, kill the 2-1 with the Mana Wyrm, and play the Water Elemental.

2. Use Coin, Kill the 2-1 with the Hero Ability, sacrifice Mana Wyrm to reduce 4-3 to 4-2, Play Kobold Geomancer.

I opted for #1, however, when I played the Coin it turned out to be Counterspell, so the Coin was lost. Therefore, I changed my plan, and killed the 2-1 with the Mana Wyrm, and played the Dalaran Mage. Black used a Cone of Cold, got board domination and went on to win. Did I screw up here?

There are couple of key questions:

1. Is it better to kill with Hero Ability or a minion?

2. Is playing the Coin against a potential Counterspell correct, or should a different spell be used?

In retrospect, I think the best move should have been:

1. use Coin
2. kill 2-1 with Hero Ability
3. drop 4-3 to 4-2 by sacrificing 1-3

This leaves the Dalaran Mage in my hand, but reduces the 4-3, so I can kill it later with a Cone of Cold / Hero combination later.

Solution 1:

It's rarely ever optimal to sacrifice your units unless you're removing something from your opponent's side of the board. They can bounce their minion back to their hand, buff it, or heal it and your plan would be ruined. So with that in mind, we remove attacking the 4/3 from the equation.

None of your plays on 3 mana are very good (the 1/4 dies easily to the 4/3), so it's a good time to use the coin. However, the secret might be Mirror Image, so you don't want to play a strong minion into it. Of course, you need to take into account that it might be counterspell and have a backup plan.

• If the coin works you could choose to test for Mirror Image by playing the Kobold Geomancer. If it gets duplicated, you can kill it with the Mana Wyrm (buffed from the coin) and you can use the 2 floating mana to fireblast the 2/1.
• Alternatively, you could play Cone of Cold and attack the Wyrm into the 4/2. The spell buffs will allow your 1-mana minon to kill the 3-mana Kirin Tor Mage and leave a clear board.
• If your spell gets countered, you can have a 1/1 and a 2/2 by attacking the Wyrm into the 2/1 and playing Geomancer or you can just have a 1/3 by fireblasting the 2/1. The 1/3 is weak against the 4/3 (if it attacks, you can't finish it off with fireblast), so I would opt for playing the Geomancer.