I have the small 1" vacuum. It works very well with any kind of substrate.
If you've never had a betta, I have to warn you to be very careful when siphoning water out of his tank. Most fish flee, but nosey bettas will get right in there. They want to know if anything going up the hose is edible.
One of my females darted right to the siphon hose and got sucked up, causing injury and nearly giving me a heart attack.

So keep a very close eye on where your fish is, and curve your fingers in over the intake part of the hose when you use it without the vacuum part!
P.S. If you choose gravel, make sure you rinse it many times before putting it in the tank, even if the bag says it's pre-rinsed.
