I personally use Kingston as I have found that they are the most reliable and compatible for use in Garmin devices of all the makes available. In over 20+ years of using Kingston I have only had one card fail or be faulty in all that time (and that includes the ones that I supply to customers).

All the pre-loaded cards we send to customers are Kingston (usually Kingston Canvas Select Plus, 32GB).

A number of customers have spoken to me about issues with their own SanDisc MicroSD cards recently; I’m not sure if this is an issue with the MicroSD cards themselves, or the newer Garmin devices being fussy, or if the issues are down to firmware or hardware issues with card reading on these newer handheld models. The main models that this issue (with SanDisc cards) occurs on includes the Montana 700 & 750 series, the GPSMap66 and 86 series, etc.

As to size, all Garmin devices that have a MicroSD or SD card slot/socket support cards up to 32GB (some older models will require a firmware update to support cards larger than 2GB). Garmin devices do not support cards larger than 32GB; so in this case larger than 32GB is not better as you can’t use 64GB or larger cards in a Garmin device as they are not supported.

As to card speed, this doesn’t make a huge amount of difference in Garmin devices. Personally Class 4 or Class 10 cards are usually fine, you can use U1 as they also seem to work fine.

Cards can be rated as Class 2 (minimum write speed of 2MB/s), Class 4 (4MB/s), Class 6 (6MB/s) or Class 10 (10MB/s). UHS Speed Class 1 and UHS Speed Class 3. UHS Speed Class 1 supports a minimum 10MB/s write speed. However UHS cards tend to have faster read speeds, usually up to 104MB/s whereas a Class 10 card is up to 25MB/s.