Some of the why on paid relays in no particular order:

- Increased reach (many clients/users only read from paid relays in global as they tend to be spam-free)

- Performance (not universally true of course, but a relay with income is more likely to invest in their infrastructure)

- Reliability (same as previous but more likely to invest their time in monitoring/keeping the relay running)

- Note retention (many public relays will clear their dbs and start over without notice if it becomes a strain)

- Contribute to a more sustainable future (if you aren’t paying for the product, you are (or will become) the product)

I won’t give you individual recommendations as I’m of course biased but if you ask around and check out the websites of various paid relays, you’ll find the right one(s) for you!