I always recommend Unicorn Trails (www.unicorntrails.com) and In the Saddle (www.inthesaddle.com) and have used both companies several times. Often, when you look more closely into any trips on offer you will discover there are several international agents agents selling the same trip - but prices vary a lot. The UK is cheaper than the US for the same trip. These two companies regularly check their overseas rides, sending staff out to ride, and when you speak to them they have excellent knowledge and make useful suggestions to help you enjoy your trip. Beyond the riding they can help with hotels, side trips etc.
Personally, I have found Portugal to be better for dressage because I really like the Portuguese way with their horses. It soft and very empathetic. I have had lovely trail rides in Spain. It is a large and diverse country, very mountainous. Both countries are a pleasure to visit.