These are my opinions and observations i have made
Sand
Personally i will never use sand BUT if you really really want to wait till your beardie is an adult.
Sand is very high maintenance to keep clean. You need to scoop out all the sand around each poop to ensure no bacteria stays inside that can make your beardie ill, and 1x month you have to remove ALL the sand and either wash and bake it or replace it.
Sand also has a very high impactation risk, especially for babies and even more so if youre planning on feeding inside the viv. It gets ingested and blocks them up, not good at all.
Paper towels
Good choice, disposable, easy to keep clean (Remove, chuck and replace). Good choice for babies which poop a lot and not very expensive.
Repti Carpet
Also a good choice, but some people have reported beardies nails catching on the carpet. Also it needs to be thoroughly cleaned regularly ro temove bacteria from poopies
Tiles
Awesome choice. I use this and the switch from repti carpet to tile was the best choice i ever made. I use textured ceramic tile. It is easy to keep clean, just pick up the poop, wipe with a clorox wipe or damp cloth and let dry. No risk of being ingested thus no risk of impactation from it. 1x month i remove them, wash them and bake them to sterilise. Also the textured tiles act as nail files to keep my beardies nails nice and short.
Another inexpensive option you didnt mention that you can try untill you decide is Newspaper.
Same benefits as the paper towels.
Here is a link to a post on another forum i came across a while back and it is very detailed on all substrates and has lots of info from personal experience
http://www.beardeddragonforum.com/index.php?threads/my-experiences-with-different-substrates.90/#post-658