You will get tons of responses on this.
A lot depends on what you like - design and even so additional items. Also, what are you riding - that makes a difference.
As an example, I have a 2021 Harley Ultra. CSC does not make an extra gas tank for their conversion on the Harley - Roadsmith does. I opted to stop for gas every 125 miles or so. My tank can get about 235-250.
CSC is a little longer and wider than Roadsmith. I also like the reverse on the CSC better than I liked the reverse on the Roadsmith. If you have a Wing, this is not an issue.
Shop around - and enjoy. Both are great conversions.