I use herptivite, by Rep-Cal, personally. It is a beta carotene product, which is important for reasons found below... I have also heard excellent things about Vit-All from Sticky Tongue Farms.
When it comes to multivitamins, most reputable brands are pretty good. What you want to keep an eye on is the Vitamin A source. Some supplements use retinol, others use beta carotene and other carotenoids.
Retinol is an animal product, essentially. It's fat soluble and as a result was at one point believed to cause issues with vitamin A overdose if misused. Now, the good news: A toxic dose of Vitamin A is nearly 100 times higher than the desired dose and is rather hard to achieve. In fact, the piece of research that first brought fourth concerns about Retinol-based vitamin supplements was shown to be faulty... In short, despite the fact that you CAN use this type of vitamin supplement to cause a Vitamin A overdose your reptile, it is very, very difficult.
Carotenoids meanwhile are plant products (hence the carrot in the name) and are actually vitamin A precursors which will be passed harmlessly is the animal aleady has enough vitamin A in it's system. The issue with this vitamin A source is that there is relatively little research as to which reptiles can or cannot convert carotenoids into Vitamin A. Generally speaking, herbivores can convert carotenoids into vitamin A, as they would otherwise not have a vitamin A source. With carnivores, however, this ability is sometimes lost - for instance part of the reason Cats need to eat meat (are obligate carnivores) is because they lost their ability to make Vitamin A from carotenoids. Now, the good news: So far, the carnivorous reptiles I know that have been tested have retained their ability to convert Carotenoids into Vitamin A, such as found this study on Leopard Geckos:
https://onlinelibrary.wiley.com/doi/full/10.1111/jpn.12924 . This means that most reptiles can convert carotenoids into the needed Vitamin A.
Now, since Bearded Dragons are omnivorous and eat both plants and animals, it is virtually guaranteed that they have the ability to convert carotenoids into Vitamin A. So, since you really can't cause a vitamin A overdose your reptile with carotenoids, using a carotenoid-based product for your bearded dragon is what I would recommend. As an additional bonus, this may brighten up your beardie's color as outlined in this reptiles magazine article:
http://www.reptilesmagazine.com/Lizard-Care/Beta-Carotene-Reptile-Color/
Hope this helps!
-Ellen