Depends on scheme to scheme. But generally the rule is that since 5 marla price is low, there is high demand for it which results in volatile prices...goes up quickly and down as well (if the society development isn't going well). But generally people make good money on 5 marla if they buy multiple files in a good scheme like DHA.
Also, Kanal plot is also good for investment as it also has high demand - mainly due to status symbol issue in Pakistan everyone prefers to have a Kanal plot, due to which its demand is always there despite having the highest price.
So compared to 5 marla and Kanal, 10 marla is not preferred from investment point of view. For actual living and construction of a house, 10 marla is an ideal space for a house for small to medium family. That's why once a society is fully developed, 10 marla demand and prices are preferred for living.
Regarding your other query, corner plot is definitely preferred over all others and the premium you pay is justified as your corner plot will always be sold at a higher price than normal ones and the best thing with them is that they are easily sold (its buyers are always high) even when there are not many buyers for the society.