On PCBs, it doesn't make much difference at all, as the fields are largely within the board, i.e. the rough, oxidized, bonded surface is where most of the current flows. If you're building micro/strip/line yourself, you can use fully plated materials of course.
Sharp corners do concentrate current more than round; you would prefer coax to stripline resonators for example. But you might justify the increased insertion loss or reduced maximum Q by the ease of construction or manufacture, and so planar filters are very popular in commercial design.
Tim