• perhaps like this?

    select case when @type1 = 'RFS' THEN

    case when @type2 = 'RFS' THEN

    case when @type3 = 'RFS' THEN

    case when @type4 = 'RFS' THEN 'ALL' ELSE @type4 END ELSE @type3 END ELSE @type2 END ELSE @type1 END