re: Big Bend National Park

Have been to Big Bend at least 10 time. The basin is grey but fills up quickly in the summer months. Also, unlike the Rio Grande Village campground that is also in the park, the basin doesn't have showers. RGV, though a little hotter as it is not up in the mountains, provides a lot more room between you and the campground next to you.

Hot springs are great as is Boquillas(sp?) Canyon which are both close to RGV campground. Hot Springs are literally right on the Rio Grande and are a great place to take off your hiking boots and soak after a long days hike. I've even packed a bathing suit.
As another poster said, the Window hike is amazing, but Lost Mine Trail is also fantastic. Neither are particularly difficult but do require a good bit of up and downhill walking. My all time favorites are Tuff Canyons and Enst Tinaja. Both provide amazing examples of different geological formations. Big Bend had lots of volcanic activity several thousand years ago. Tuff canyon is formed from dozens of feet of hardened volcanic ash being carved out by water. a great half day hike. Ernst Tinaja is kind of a hidden gem in the park. Not many people traveling down Old Ore Road to get there. Also, the road getting to the Tinaja can often be a bit treacherous.

Going in the summer is great but it will be very hot during the day and cool at night. I've been an equal amount of times in winter and summer. Any time of year is a good time of year to go.