Keep it simple! Use one single reed for all your sounds, this is very important during those close encounters, it's no time to be fumbling around your pockets for a specific reed for a specific sound. My two favorites are the Mistress & the All Star, both have their pluses & both are great. They are great for making every sound a cow or bull makes. You can sound like any sized bull you'd like to with enough practice.
When using a Bugle & Reed for Location purposes I try to to hit the highest note possible so it is far reaching, I'm trying to locate elk at this time not call them to me, you need a fairly tight stretched reed to accomplish this. When Advertising or Challenging Bugles are needed these same two reeds are great for this as well. Be as big as you possibly can when imitating bull sounds within reason, this means don't blow your reed out or over blow your bugle to where you start losing believable tones. Most hunters are not nearly as big sounding as they think they are especially after a 100 yards+ away from other elk. This is why it's good to sound as big as you can in a controllable tone. Big does not always mean loud, it's all about the sound choice you choose that can demonstrate to other elk if you you are a somewhat mature bull. For the most part bigger more mature sounds are better to other elk, it's more believable. Bulls do not walk around in the woods thinking they need to sound small so they do not run other bulls off & neither should we! (grin)
So, choose a single reed like the All Star or Mistress & you'll be well on your way through practice with some awesome elk calling! Good luck!
ElkNut1