How close to each other are they?
If they're within 100m I'd use a copper SFP, not fibre, because they're cheaper.
If they're 100-220m apart I'd go with multi mode fibre (MA-SFP-1GB-SX)
If they're over 220m apart, up to 10Km, then it's single mode fibre (MA-SFP-1GB-LX10).
Of course, make sure you align this with whatever you actually have for your structured cabling between the switches if they are not in the same location. E.g. if you have single mode fibre between two wiring closets then just get the LX SFP's as the other won't work well over that.
https://meraki.cisco.com/lib/pdf/meraki_datasheet_sfp.pdf