It depends on how heavy you are, but a 25mm training tire is fine for general road riding. If you are very heavy, then go for the 28. Depends on the width of your rims too. A true 28 will fit, but it might not give you the best handling on the typical narrow road rim. I've ridden the same bike with 25's and 28's. The 25's seem a lot more snappy to me. But to be honest, I didn't think there was that much difference. But for a period bike like that, I suppose you might want a wider tire similar to what might have been on the bike originally.