Any opinions on whether September or October would be better for visiting Barcelona and Madrid? I've checked average temperatures and it looks like, obviously, October would be a little cooler, but not a real big difference. Any considerations other than temperatures?

Other consideration would be local or national Holidays as they can have a noticeable impact on your sightseeing and prices. Barcelona has local Holidays on the 11th and the 24th September. The 12th October is a NATIONAL Holiday. I would try to avoid those dates, especially in Barcelona where Holidays means either crowded or closed main sights and even more chances to get pickpocketed (worst city in the world for this type of crime). If it was me the deal breaker would be when is it LESS crowded? I would go with Oct.

One of the biggest festivals of the year in Barcelona is around the 3rd - 4th week, La Merce. It will be more crowded than usual but it's also a great time to visit and see parades and typical Catalon festivities.

And I probably wouldn't be able to get a hotel reservation on September 10....
thanks Viajero and Cathy; looks like my decision has been made in favor of October.

You shouldn't have any problems finding a hotel in Barcelona in September during La Merce. The city has more than enough hotel rooms and prices typically do not go up much at most hotels, if at all, during the 5-day celebration, but many hotels do increase their prices whenever there is a convention/congress in town.

Our only visit to Barcelona we stayed at the Hotel Colon. It overlooks the cathedral. We were in room #305 and had a great view. Our trip was in late February and the weather was in the high 60's, low 70's during the day. Nights cooled down a bit. Weather in October would probably be a bit warmer. www.hotelcolon.es For info www.maribelsguides.com http://en.wikipedia.org/wiki/Barcelona

We were in Barcelona in late October of 08 and it was gorgeous, sunny and mild weather. It sprinkled rain twice in 8 days but it was very light a never lasted long. For the most part I wore a velour zip hoodie jacket during the day and most nights. On cooler nights I had a thin wool jacket. Its a beautiful time of year.

Thanks so much, Robert, Iris and Giulia, for your additional thoughts. I'll definitely check out Hotel Colon, and I appreciate the weather and jacket info.

And next door is their cheaper version called Hotel Regencia Colon, also a good hotel. Couldn't be a better location.