In a better sushi bar, everything will be fresh, or the chef will warn you apologetically if you order something that he is not particularly proud of that day. It might prompt him to tell you of something special that is not on the 'menu', or he may not appreciate the inquiry. When checking out a new sushi bar, I try to order a few things that tend to be good only in the better places. If you don't care for these things, just order what you like and see if it measures up. Size is not necessarily a measure of quality or value.
Some shops serve small portions of very good fish, some serve small portions of poor fish.
Naturally, large pieces of good fish are a good value, but judge the quality on taste, then worry about the cost per pound when you get home. The size of the fish should be proportional to the size of the rice, that's just good sushi balance. Some places give you rice that is too big for the fish. If you want to fill that last corner of your stomach without breaking your budget, order tamago and a cucumber roll. The rice mounds should be firm and smoothly coherent.