Exalate allows syncing any kind of custom field type combination.

This article shows how to synchronize a select list with a user picker field.

For example, you have a custom field called userlist (select list Single Choice) to the custom field Escalated to (user picker field). 

Sending side

Data Filter 

#
# Include the customfield 'usersList' in the message sent to the receiving instance
#
replica.customFields."usersList" = issue.customFields."usersList"
...
 

Receiving side  

Create/Change processors

# 
# The replica.customFields."usersList".value is an object of type option. 
# The option contains a value, which is the string of the option.
# issue.customFields."Escalated to".value is a user picker type custom field, which includes string value
#
issue.customFields."Escalated to".value = nodeHelper.getUserByUsername(replica.customFields."usersList"?.value.value)

...