When in doubt, aks fellow pilgrims for suggestions: which is what I'm doing right now...

More statistics than you may want! It has annual and monthly data, and shows the starting points, the camino, ages, gender, country of origin, etc.

https://oficinadelperegrino.com/en/statistics/

Hi Andre
I started in Lisbon in 2016 in early September and had to skip part of the Camino before Porto because of the heat. Some walkers had heat stroke although each year can be different.
Then walked the Central Route to Santiago. A lot of road walking and not particularly pleasant.
In 2017 in September walked the Seaside route from Porto including the Spiritual Variation. Much more enjoyable walking surfaces and the sea breeze keep the temperature down. Note this was NOT the coastal Camino which is further from the coast. If you want a shorter Camino this is a good one.This year in April I started in Seville on the VDLP which exceeded my expectations with generally great walking conditions through fields, woodlands and crops. Due to the rain all was very green. Don't know what it will be like in August but I expect it will be hot. As Jasper K said the distances can be a lot further between villages however there are some wonderful historic towns dating to Roman and pre Roman days. It is 1000 km in total. I did around 500 km to Salamana. So it may come down to fitness and time availability.
Hope this helps
happymark

Believe @happymarkos did a good job of explaining the differences. They are two VERY different Caminos. I have done all of the routes from Porto and would agree that the Litoral is the most scenic. Actually the Litoral weaves back and forth with the Coastal which is not really on the coast although you see it from time to time. You go through many beachside resorts on the Litoral so I can imagine that it will be quite busy in August. Probably a lot of pilgrims too.

I personally did not like the Interior - way too much asphalt and other hard surfaces, also the first few days out of Porto are along busy roads. I wouldn't do it again although Fernanda of Casa Fernanda and her family are lovely and others do like it. All three of these routes meet at Redondela and follow the same Camino to SdC.

The Plata will be dry and hot for sure. I have walked it in June, July, October and February and as I have mentioned in other threads there were only a handful of pilgrims walking when I did. I do well in the heat and can walk long stages so it has never been a problem but you will need to carry at least 3 liters of water. When I walked in July I had a 2 L bladder and two 500 ml bottles and I actually needed more. To be graphic, I never had to pee while walking - not once in the 3 weeks walking from Sevilla to Zamora! Which of course is a sign that I wasn't getting enough. I would drink another liter when I arrived at my destination.

So I would say depends how you do in the heat and whether you would rather have a more solitary walk.

Ultreia
LT