Thread:Knj00/@comment-26883673-20161223033558/@comment-5089372-20161224022718

If your goal is to just level up as many as possible then yes, cheapest ones first is an ok way to get that done fast. However, if your goal is more about getting some good fighters for the arena then you may want to pay attention to certain types (lots of people list these in the Battle Arena page comments) and focus on feeding them because some of them do take a lot of food.

The level 10 or 15 is again really only something that impacts the Battle Arena (and earning rates). If you take a look at the calculator on the Battle Arena page and use the "Find Best Matches (Levels 7-15)" option you can see the difference a level 10 dragon vs a level 15 dragon can have. Sometimes this difference can give you an advantage.

Personally, I only level dragons up to 15 that I use the most in the arena. I leave the others at level 10 because I feel it is a waste of food taking them to 15 since I don't need them in the arena and the extra coins are irrelevant because I already have a lot.

Feel free to ask others these same question if you want on the arena page or the forum here. Many different people have different playing styles and it may help you to get different opinions.

I hope this helps! :)