Assuming you don't need HLL. Hit Area would be the best option for clearing spawn with Whirlwind, or if you're also using Doubles for Double Strike on a boss then I'd go with HLD for two reasons; it'll proc more than M&S glasses letting you Onslaught/Double Strike easier, and, on bosses having Hit Spell is sometimes a bad idea because they have Counter Attacks that trigger more with delayed or damage over time effects going off.
In some cases it may be beneficial NOT to match the Hit Area type with the weapon's elemental damage type and have the opposite (for example a 100% cold damage weapon with Hit Fire Area) such as with the new Champ Spawn coming out that has monsters that have 100 in all resists except fire or cold, (ignoring the option to use Consecrate on templates with Chivalry) it would give you a method of damaging the other monster type that is spawning at the same time.
