I bought the Continental 1.752.5 MTB 26 tubes with the Presta valves to install with my Michelin Country Rock 26 1.75 tires that I bought at WesternBikeWorks. I store my bike in my home, but I haven't had to add air in the tires for 3 weeks and the pressure is still the same. With my old tubes, I had to add air weekly. These tubes have exceeded my expectations. Will buy again!
Reliable quality and competitively priced. They last and last but replacement is eventually necessary. It's not if but when.
The 25-32 size is really handy because it covers the sizes most commonly used on road and gravel. The 60mm length is perfect for the slightly aero rims I have, no need to mess with extenders and moving valve cores.