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Best spawnpoints- Lair, Graveyard, Gate to voltary. They have enough health and armor to survive.
2nd type of good spawnpoints- Vine tree, temple of asyra, Libro Mortis. These are cheap creature spawnpoints, and casting them doesn't commit as much mana as other spawnpoints.
A pentagram is horrible against wizards and forcemasters (but otherwise quite nice).
Barracks is a bit confusing. You cast it in the back and the garrison posts in the front, and you can even wall it off since garrison posts don't require line of sight, but it is still a relatively vulnerable spawnpoint that opponents tend to focus down (since that would also make your garrison posts less useful, and they are part of the investment as well).
About trying to destroy spawnpoints-
If playing a warlord, then I have akiro's hammer, which is the ultimate conjuration destroyer. Even if you get only one shot and your opponent immediately spend his resources to make sure you wouldn't get a second shot, the first shot is like a force hammer (9 mana commonly used attack spell) so for 3 mana (or 0 mana if you have a construction yard and get 3 mana refund) it is definitely worth making the opponent spend the resources to kill 11 life 2 armor. These are a lot of dice not rolled against your mage
Casting an acid ball to lower armor before further attacks are made is a useful strategy (with all mages).
With other mages, sometimes focusing the mage is easier than focusing his spawnpoint.
