I have building kodi boxes based on raspberry pi for years and have always used the original XBOX DVD remote (because thats what I used when running XBMC on the original XBOX) but they are becoming harder to source and need a special cable.
Anyway, these are the 3 different types that I use at the moment
(a) XBOX DVD Remote
This is a natural fit for Kodi and I like the way the remote feels in my hand. Some people dont like the thought of taking up a USB port. However, on the plus side, the cable is quite long and can be situated with the IR dongle on top or below the TV.
You can source the remote on amazon or ebay and the cable is available on ebay.
(b) Toshiba MCE Remote
This is designed for the Raspberry PI and does not take up a USB port. The receiver sits on the GPIO pins (you may need to drill a small hole in your raspberry pi case depending on the case used. The range is not as good as the XBOX DVD remote but it is small and neat. Is available for about £5 from banggood.com
(c) Generic USB remote.
Some people swear by these, but it feels cheap and nasty to me. Available from ebay for about £4 but I only use it in emergencies.
I have discounted using a flickr remote because I dont want to buy a remote thats almost as expensive as the raspberry Pi itself.