Well, I get 2 LA knocked off for "free", so I'm happy with half-dragon, unless you all can suggest something else with a similar strength boost. I don't think the breath weapon matters for much -- it's only 1/day. At this level, with the mantled warrior substitution level, I should be able to summon a +1 weapon with whatever other +1 mod I want -- next level, I get two +1 mods that I can combine together or leave separate, as I want, for free. I can pay a few pp to augment it further, if I needed to.
I'm thinking that mostly I'll have some sort of elemental damage, like thundering fire or something, unless I need to swap those + bonuses for ghost touch (+2 bonus) or something. That should let me switch around what the bonuses are on the weapon in case some creature is immune (or it's that one monster that gets boosted HD from electricity damage.