I am interested on knowing what would be a better solution to create a current source for low current applications (below 20mA), an opamp based current source such as a Howland current pump (link to PDF) using closely matched resistors, or something like a transistor based current source such as Wilson current mirror using matched transistors in a single package.
I am aware that there are a lot of factors that should be considered, to start with, the types of opamps used, the type of load, bjt vs fet, voltage compliance, etc... So in a general way, what I would like to know is if its worth looking into a transistor based solution, does it offer any advantages over opamp current sources in low current applications?, or should one just stick to opamps for simplicity?