If your view of international trade is framed by the dichotomy of protected national markets vs. global free trade, then bi-lateral trade agreements and regional trade blocs look pretty much alike: an in-between situtation involving liberalization of trade within small (two or more) groups of countries, beyond whatever has been agreed at the global (WTO) level. Standard trade theory evaluates both by weighing trade creation (within the group) against trade diversion (trade that other countries would have had with members of the group, had the bi-lateral or regional agreement not gone into effect).

If, on the other hand, you see regional blocs in the developing world as instruments for the growth and empowerment of poor countries (h/t Norman Girvan), it’s a difference of night and day.