[Parasite]

I always load heavily shielded troops first. If any troops survive, they always include the shielded ones. Even at loss rates of up to 50%, only rarely have any died.

Once an enemy dropped troops on my planet. He is a good player and would have loaded his people correctly. Yet, everyone of the assault wave died except most of the strongly shielded troops. They had no weapons and so I was able to extend the planetary battle for over 5 turns effectively trapping his fleet around the planet.

The best troop mix could be found using a Game Theory Equation. A combined arms mix of small, large and medium troops with different ratios of shielding and weapons exploiting the "Leaky Armor" effect SJ mentioned.

For organic races the minerals and build time saved by not putting on the relatively heavy shields means you can have three or more times the troops if transport is available. I just use it on the leader classes. If ground cannons or other mineral weapon is used the shield weight percentage is less and leads to a mixture possibly being the best way to go.

The basic truth is that you can never have too many troops. Send all you have (with at least one or two leaders for ECM/ECCM support) Any surviving will help the planets morale recover that much faster.

As the saying (and sig) goes...
There is no Overkill... Just the word "FIRE" and "Reload".