I will be visiting Barcelona in early August -- 2 full days and 3 nights. I plan on visiting the Sagrada Familia during the morning of our first day. My question is: should we do Park Guell the same day or do it the morning of our second day? Considering the expected heat, I am anticipating that it will be better to visit these sights in the morning. But I also understand that both sights are situated near each other which might make it more "time effective" to see on the same day. This forum has been invaluable to me in planning my first ever trip to Spain. Thank you in advance for all your help!
Check out my advice here. Look at WED16: http://www.tripadvisor.com/ShowTopic-g187497-i44-k7350676-First_Timers_Help_With_5_Day_Itinerary-Barcelona_Catalonia.html#57433425
and regarding the recommended DIY walking route: http://bit.ly/DIYroute-pg-sf
As a broad plan, and from your initial ideas, then perhaps look at ...
Day 1 - Park Guell >> Sagrada Familia >> Montjuic
Day 2 - Passeig Gracia (Casa Mila or Casa Batllo) >> Ramblas (La Boqueria) >> Bari Gotico (Cathedral) >> El Born (Santa Maria del Mar) >> Barceloneta (beach)
When we went to Parc Guell in 2011 it was hot as hell and very uncomfortable.
One thing you need to consider is that Parc Guell is at the top of a hill, and I think that walking there would be a challenge.
My advice would be to go to Parc Guell first thing, before it gets too hot, then walk downhill to Sagrada Familia.
Finally, if for whatever reason you have to skip one, skip Parc Guell. Sagrada Familia is incredible, do not miss it.
Enjoy!