In the last few months, Digi-Key has been receiving a fair number of calls from folks asking for resistors and/or transformers for use with ring brand video doorbells, and it seems likely that many are finding DK through this page on the support.ring.com site.
are recommended by the ring product team for use with their equipment, and folks have been asking about the difference between the two.
Both are within ring’s recommended window of 25~33 ohms resistance, and 20~50W power rating. The FSOT30-25-ND measures roughly 1.25" x 1" x 0.6" and has some fairly convenient mounting holes, whereas the FVT50-25-ND is rather more cumbersome at 0.56" diam x 4" length. For the simple reason of physical convenience, the FSOT30-25-ND is likely the better choice between these two.
A related question along these lines is “Where can I get a suitable transformer?” All of these fall within the recommended output voltage range of 8~24VAC and come in a convenient plug-in form factor. Among them, the HM1574-ND would probably be a good first choice, as it lands nicely in the middle of the recommended voltage range and ties with several others in the group for lowest list price.