We've been using two-hit minions with some success at our gaming table. I aim for hit points such that the fighter's at-will would kill it with a weapon die roll of 8. (e.g., maximum damage with a longsword). So, a crit kills. Most Encounter powers kill. Most At-Wills reduce more than half their hit points.
It addresses the "Hey, only one party member can kill them" problem: everyone can kill them, it just takes two shots.
In that context, Resist 5 and Vulnerable 5 have huge impacts on the toughness of those minions. Vulnerable 5 tends to mean "Use this type, and they're one-hit minions". Resist 5 tends to mean "Use this type, and it'll be three or four hits instead of two."
That works for me.