I mostly use 3 aluminum alloys. 6061-T6, 2024-T5 and 7075-T6. Each has particular advantages.
6061 is the most available in almost any shape. It is also the least expensive. It is easy to anodize with consistent colors, even in a crude home anodizing set up. It can be easily welded.
2024 is much higher strength. It costs about 80 percent more than 6061. Machines very nice as it had a very crisp chip. The high copper content makes it harder to anodize and is difficult to weld. Yield and ultimate strength much higher than 6061.
7075 is the highest strength common alum alloy. Yield and ultimate strengths almost double of 6061. The strength falls off at elevated temperatures so is not a good choice for high performance pistons in model engines. Machines very nice, similar to 2024. More difficult to anodize than 6061, but not as difficult as 2024. Not good for welding. Cost is about double of 6061.
None of the three are really happy about being formed or bent. Other alloys are much better for this, but don't machine well.
For a brief overview of these alloys, go to:
http://www.onlinemetals.com/aluminumguide.cfm
Gail in NM,USA