I own both lenses, they are both excellent with a different and distinctive signature.
Planar has slight resolution advantage especially on wide apertures and perhaps more important, smoother transitions to oof areas and smoother bokeh too.
Tessar has more contrast and a more punchy rendition on the focus plan, that gives its signature especially in black and white images.
While the best would be having both so you can understand what lens suits you the best, I suggest doing a search online for images made by those lenses to get an idea of their different characters