I own both a Planar 3,5F and a Tessar. MY Planar is much sharper than MY Tessar at all apertures, not only wide open.
Bokeh is fine with both, nicer than many other lenses in MF.
There are other optical issues to consider, such as field curvature, where the Tessar is not so great.
Overall I would go for a 3,5 Planar any time, finances allowing. Remember that you can also get the Tessar in a Rolleicord- that may be the best budget option.