I would recommend a slate call with a wood pot and variety of strikers. They vary in price these are some of the best I've used.
Cane Creek Custom Slate David Halloran Slate They come with strikers, but I carry a couple different ones, the striker can really vary the pitch and rasp of your call.
Halloran Purple Heart Woodhaven Birch Laminate There are cheaper ones out there, such as the Primos Jackpot w/ Slate (not sure if this is still made, when I bought it it was around $30) that will work but the Halloran and the Cane Creek sound better to me. Once you are proficient you can add different strikers and friction calls such as glass, which gives a sharper sound than slate and works in wet weather.
Mouth calls are wonderful but have a steep learning curve to be proficient, if you have used one before for Elk it may be easier. Box calls are easier to use, and easier to cut and call louder, but only make one sound, the pitch and rasp doesn't vary much.
I carry a variety of calls with me these days, but if I could have only one call I would take a Slate call and that Woodhaven Birch lamanate striker. If I could have two, I would add a mouth call, specifically the Primos True double. It took me a few years to get good with the mouth call. I would suggest getting one to learn but keep it at home until you get proficient. It's a rare day where I can't get a response back using either the slate, glass or mouth call. Some days they like one, but wont have the other. It can be as simple as a striker change to either get them to come or run away paranoid, so it's important to have a variety.
This is the glass call I use
Cane Creek Glass call