Personally I have found that higher gravity beers on certain beers can produce undersized and irregular yeast cells with monumental cell counts. I would preferably pitch a 'healthy' top cropped yeast in to a low grav beer but then again I have the option to do this.
Back to the OP It depends on the yeast and what you are trying to do with it. 90% of the time I take from krausen, 10% wash yeast from the bottom 'cake' but fully expect to have a slow ferment on the next beer pitched with this. The yeast I used has had this had this treatment for the last 15 years with no infection or recluture.
In home brew terms go for the krausen skim.
D :thumb: