You should not choose weighting based on variability you happened to observe in one small experiment. Random scatter can cause some SD values to be high and some low, and these differences may not reflect consistent differences in variability. Don't weight by the SD of replicate values, unless you have collected data from many replicates. To weight by factors you calculate using GraphPad Prism, choose the option to weight by the reciprocal of the standard deviation squared. Prism minimizes this quantity shown below.
Prism also considers sample size when weighting.
If you entered individual replicates, and chose to treat the replicates separately, then no special calculations are needed. The means computed from a large number of replicates get more weight than means computed from a few replicates.