For me when I look for a new suitcase I always look for empty weight no more than 4kg, soft sided and with wheels/folding handle plus I buy a luggage strap. As well as a weight allowance keep in mind airlines also have dimension allowances for luggage based on total added together of height/width/depth. Excess luggage charges are often excessive revenue generating charges , often by kg so follow canuck78s simple advice on weighing luggage.