A few factors to consider when choosing tournaments:
Popular tournaments can fill early, and may need to be reserved 8 weeks or more in advance. The main risk is not getting in, rather than it not filling or the competition being questionable.
Less popular tournaments you may wish to contact the organizer to gauge how it is filling up, and which teams have committed (making sure you have good competition) before reserving a spot. These tournaments can sometimes get cancelled or have age brackets get combined, so proceed more cautiously and open up a channel of communication with the organizer. The PRC tournaments this year fit this category as they are new. May want to have a backup plan identified in advance in case it falls through 1 or 2 weeks prior.
Use Tourney Machine (may have to Google for prior years) to find which teams participated the prior year if gauging popularity and competition level. About 25% of tournaments use the tool, typically the DSM higher quality tournaments. https://www.tourneymachine.com/Home.aspx
Leverage coaches from the 6th, 7th and 8th grade teams for insights on tournaments. They will gladly share their perceptions and experience with most of the ones you are considering.