It is always recommended to modify the geometry to make 6 side face rectangular/square cubes so that hexahedron element can be used. Hexahedron mesh is good for less no of nodes/element count hence less computational time and less stiffer than tetrahedron elements.
Slice the upper and lower flange and mesh it with multizone/sweep method for hex elements. If you want to, you can directly use automatic method which either sweeps if body is sweep-able to produce hex mesh and if not meshes it with tetra elements. Hex dominant method produce mix of hex, tetra and pyramid cells and used when the geometry is not multizone/sweep type or cannot be meshed with hex elements to keep the mesh count less than tetra elements.
Meshing is also depends on the type of analysis you want to perform. For static structural analysis hex (is best) or second order tetra mesh is sufficient.
