Gilded Infusion or Magical Infusion?
This is a good question but I am afraid which one is better is pure opinion/speculation.
Here is the official wiki link on Magic Find. http://wiki.guildwars2.com/wiki/Magic_find
“Everytime you kill a monster you roll on a number of tables, inside these tables are different rarity categories. Magic find increases the chances you will get higher categories. For example if there is a 1 in 10 category, and you have 200% magic find you will have 3/10 chances to get that category. This improves not just the rarity of the items you get but can also improve your chances at getting trophies and rare crafting materials like lodestones.”
This implies that there are no diminishing returns and that magic find still works beyond 100%. And it states that yes it does help find lodestones.
gilded is probably much better. Especially if you do dungeons.