none (if you're advanced and terrain-focused)
A-Basin is definitely a place best-suited for the advanced skier/rider. You're not going to get all the bells and whistles of the major resorts (and their associated crowds) or an apres-ski scene. What you will get is some excellent downhill terrain. On to the details...
Parking is right at the base of the mountain, no need for shuttles or a long walk, which is great. We went on a Monday and it was EMPTY.
The main lift from the base is high-speed, which is great until you get to the top and realize you're only halfway up the mountain and have access to maybe 5 different runs. All the other chairlifts are slow. Once you've made it to the top, you're faced with decision of heading back down the front of the mountain, or dropping down the back into Montezuma Bowl. This is an easy decision. The half dozen or so blue runs at the top of the front side of the mountain are really just one wide-open snowfield since it's above the treeline. They're great when you're looking for a cruiser at the end of the day, but otherwise very boring.
Montezuma is not. Other than a little bit of steepness at the top, the blues are pretty true to their rating in Montezuma, so no need for the intermediate to shy away. A word of warning for snowboarders: keep your speed up on the end of Larkspur. There's a large uphill part that you can see coming well in advance, but it's easy to keep your speed up for that one. The tricky part is after that when you turn through the woods and can't see that uphill stretch coming. I was a little disappointed in the brevity of the glades, but the powder on the walls made up for it. You can traverse far enough on the walls without hiking to hit the good stuff, and you only open yourself up to more powder if you're willing to put in the effort to hike. The wall on skier's right has great steeps; the left is more gentle and has some nice (but short) parts through the trees.
Black Mountain Lodge is your lunch destination. Quality food that's still expensive (but not as much as the mega resorts) and... reasonably priced beer! Which comes in handy if you need to get your nerves up for the runs off the Pallavicini lift.
This was hands down my favorite part of A-Basin. I'm an advanced, but not expert snowboarder, but I was able to handle the Pali lift. If you're fearful like I was, try Main Street or the Spine first, since they would be more appropriately labeled as double blacks than extreme. If you can handle those runs, then head to skier's far left to challenge yourself in the glades or to skier's right to find the bumps. I spent the whole afternoon on Pali until my legs finally cried mercy. It was amazing.
And one last little thing I loved about A-Basin... the views. If it's clear, you can see Keystone and Breck from the top. Even if it's not, the immediately surrounding mountains are just so dramatic and beautiful. All the Colorado resorts have great views, but this one just stuck out to me for some reason.