For proper Bloodtalons usage, you want to buff the abilities that will do the most damage per cast, also known as damage per execute (DPE). In a single target scenario, this is easily done by using it on your finisher and Rake (which will be your second most damaging ability). However, with more targets the priority will change.
This spreadsheet will provide both the DPE and damage per energy (DPR) for all abilities including talents. You can use the Sabertooth and Soul of the Forest (SotF) dropdown menus to select whether or not you are using those talents.
There are multiple ways you could use the information provided in this spreadsheet, but the two main usages are for:
Prioritizing Bloodtalons to buff the most damaging abilities at a certain target count
Priotizing abilities with a higher DPR first (general usage, not specifically with Bloodtalons)
Note that due to Primal Wrath doing a lot of damage, the data points on the chart will be out of the vertical axis bound - in other words it is very good for AoE.
Azerite traits are not included in this spreadsheet
One helpful rule of thumb that can be taken from this spreadsheet is to use Primal Wrath in place of Ferocious Bite at 2+ targets without Sabertooth, and 3+ with Sabertooth just for its initial hit damage.