Renewal rates are definitely something I pay attention to. A low first-year registration price can drive impressive growth numbers, but if a large percentage of those domains aren't renewed, it suggests many registrations were driven by price rather than long-term intent.
That said, I don't think renewal rates alone should determine whether a TLD is recommended. It really depends on the customer's goals. For a local business, startup, or personal project, a newer extension that fits the brand well may be a perfectly good choice. For a business making a long-term investment in SEO and brand recognition, I still tend to encourage securing the .com whenever it's practical.
In the end, I'd rather recommend the extension that best matches the customer's objectives than simply the one showing the fastest registration growth. Growth can be driven by promotions, but sustained renewals are a much better indicator of real adoption.