Best Bit for Eventing Mare?

Okay, so I'm looking for a new bit for Desi. We mainly event, but we will be doing a little Dressage and Jumpers for training/fun. When we go xc jumping she is more excitable (she loves it!), so her eggbutt snaffle doesn't really do much good. She breaks at the poll just fine, and she's amazing on the flat (just a little forward moving, but once you get her warmed up she's awesome), jumping she likes to rush the jumps, but we are working on that. On xc she will go to the jump fine, then when we and, she will take off. She has problems turning on hills and likes to turn to the outside when circling.

--equinegirl26

P.S.
I like this bit. Myler Low Port Comfort Snaffle Horse Bit MB 04 | Dover Saddlery

ETA- I've used the bit above on young, green horses and I love it.

Looks similar to an elevator with some noseband action. Have you tried a regular elevator with her?

Do you know anyone who would let you try some different bits before you buy? You could end up spending a ton of money before you get the right one or you mught be lucky first time - its a lottery.
I have had horses that didn't jump so well when they were changed into a stronger bit especially if you make a big leap from mild to quite severe.
Sometimes a thinner snaffle is enough to do the trick

This place lets you rent bits and try them out for a little while. If it doesn't work out the way you'd like, you can send it back! Plus, they have pretty helpful "specialists" who really seem to know their stuff about deciding on a bit best suited to your specific horse and circumstances.

Treeless Saddle Demo Program - Myler Bits Rental Program - Myler Bits Gold Star Dealer

Okay, I will look at that.

Equiniphile: No, I haven't. :)

The best and worse bit is determined by the riders hands. A harsher bit is not your answer. Work on making your contact light, get collection with your seat and legs. If your trainer cannot help with this, get a new trainer, not a new bit.

This is all well and good, and I agree that a rider should work on making their horse more adjustable and attentive, but sometimes a responsive horse in the ring can still get excitable and might need a different bit. Note that I said different, that doesn't always mean harsh or stronger, just something that works differently in the horse's mouth.

OP, I think you should perhaps try a thinner snaffle first before phasing out the snaffle for cross country. I suggest a Myler level 1 loose ring. They're fairly thin and if she goes well in that then great! A Myler combination is a bit strong to automatically switch to. From your description, it sounds like she's just running through your hands and ignoring you. Do what stevenson suggested and really work on her attentiveness and adjustability outside of the arena. I don't think she needs an elevator bit, just something with a little more oomph to get her attention.

If I were you I'd try a fat, slow-twist full cheek, keeping in mind that it's definitely more bit than you're probably used to and you need to be very careful with your hands. Does she pull down at all? Or is she just ignoring your direction and not turning when you want her to?

She doesn't pull down, but she's ignoring contact.

I used to use a copper eggbut snaffle on my super rowdy tb, but he completely blew it off. So, for training purposes I used a kimberwick for a while... but the important part is that I used DOUBLE REINS! I can not stress this enough. What you do is ride strictly on the rein that attaches to the snaffle mouthpiece. When my horse would start getting too hyper and not listening, I would tighten up on the rein that connects to the curb chain. This usually got him to listen up real quick. As soon as he responded, I would loosen the curb rein again and ride only on the snaffle rein. This taught him to respect the snaffle more, or else the curb would come next as a reinforcement. I (and several other people at my barn agreed) believe that this is a great tactic because, because of the individual rein usage, you give the horse the chance to be good before you "haul off" on the curb chain.

* But an important reminder: if you've never ridden in a curb chain and/or double reins, GET HELP FROM SOMEONE WHO HAS. Improper use of either can result in injuring the horse's jaw severely!