Spain or Budapest/Prague in October?

You don't have to be concerned with flood damage in B. and P. It was small considering the size of both cities. I would take Spain trip because I haven't been to Spain yet.

Weather will likely be better in Spain- a bit warmer, and much of Central Europe lies under overcast gray skies in the fall. But you could still have a fabulous time in Prague and Budapest, both great cities (Budapest especially in my book). Neither Budapest nor Prague suffered much damage from last month's floods, and you probably won't see any evidence of it in October. Demonstrations in Spain are nothing to worry about- almost always peaceful, and no danger to tourists whatsoever.

I have been to both locations and I would say either option is a good choice. Both completely different but each with its own beautiful sights to see and culture to experience. Given the time of year however, I would probably choose Spain for this trip simply because you might get some nicer weather. Once you choose you can gets lots of good advice here on sights, lodging, logistics, etc. (If you do choose Spain I would try to add a few areas further south)

Unfortunately I've not been to either area so can't address that question, but for what it's worth:
If you plan to go in early October the weather in Prague and Budapest will be approximately the same as Berlin and Munich (as likely to be sunny and mild as gray and dreary). Many on this forum like to travel in October to these locations. If you truly just want warmer weather, then you should choose Spain. However if weather is not a prime mover in your decision then you should leave it out of the equation and make your choice based on research and advice about the various cities you mention taking into account your personal travel wants & likes (scenery/architecture/local food/history etc).

Or you could base it on Spain's 25% unemployment and greater need for your economic contribution. I'd pick Spain because I haven't been there and was in Budapest/Prague last year. But that has nothing to do with your choice.

i was in san sebastian, bilbao, barcelona, cordoba, sevilla and ronda last october. i was surprised that it was a coveted vacation time for british and central europeans. it was roughly 70 to 80 up north ending in 85 to 90 down south. it rocked. i have only been to budapest and prague in february and march and it snowed both times which was awesome. october will not do this. go spain and have a great time. have fun, be safe.

One other thing to consider: futbol! If you are a fan, then go to Spain and see some of the teams play in all three cities you mentioned. On the other hand, I have been to Spain and plan on returning, but Budapest is where we will probably go next (after stopping in Barcelona for a game or two first:)

Thanks for all the advice! I am all set for Spain in October!