The Content Manager user options allow you to sort Record Types, how do you achieve this using the SDK?

First you want to find our whether the option to display your favourite Record Types first is switched on, and if not to switch it on (or off).

var options = new TrimUserOptionSet(db, UserOptionSetIds.SelectRecordType);
var favFirst = options.GetPropertyBool(PropertyIds.SelectRecordTypeUserOptionsFavoritesFirst);

Console.WriteLine(favFirst.ToString());

options.SetPropertyBool(PropertyIds.SelectRecordTypeUserOptionsFavoritesFirst, !favFirst);
options.Save();

Next you will want to make one or more Record Types a favourite for this user and then move it up or down in the list.

var recordType = new RecordType(db, "Document");
recordType.AddToFavorites();
recordType.ChangePositionWithinFavorites(LabelPositionChange.MoveUp);

Retrieving the Record Types in the order specified can be achieved through either the SDK or the ServiceAPI. Using the SDK requires a TrimMainObjectSearch constructed using the RecordTypeFilter enum, for example:

var recordTypeSearch = new TrimMainObjectSearch(db, RecordTypeFilter.AllForCreate);

The ServiceAPI requires the parameter recordTypeFilter, for example:

https://acme.com/ServiceAPI/RecordType?q=all&purpose=2&recordTypeFilter=2