All antibodies listed here have been tested on 2x10^6 (two million) cells using the eBioscience™ Foxp3 / Transcription Factor Staining Buffer Set. I have not done much testing with the BD equivalent, but it seems to behave similarly. For human, another good option is to use the BD Cytofix/Cytoperm kit, staining overnight in the perm/wash buffer in the fridge. This typically does not preserve as many epitopes as the Foxp3 kit, slightly higher concentrations are required, and it does not work as well for nuclear proteins. Note that each antibody should be titrated for best results and that the approximate dilutions listed are only a rough guide. The precise dilution factor scales somewhat linearly with the brightness of the fluorophore if the conjugate of a particular clone has been prepared well.

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Note that for overnight surface staining on unfixed cells, essentially all antibodies work. The optimal dilution factor is typically 2-5x less than for a 30-60min stain.

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For human, pre-blocking for 15-30min prior to overnight staining is essential. Mouse serum at ~3% works well; this may be combined with rat serum and/or commercial Fc-blocking reagents for most purposes. You may find that just adding the block to the staining mix is adequate.

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Note that some fluorophores can be problematic when used intracellularly. This isn't true for every conjugate of that dye, but is more likely to be an issue with these dyes: APC-Cy7-type tandems (APC-Cy7, APC-H7, APC-Fire 750, APC-Cy5.5, APC-R700, much less so with APC-Fire 810), PerCP-Cy5.5 (less so with PerCP-eFluor 710), eFluor506, BB630. NovaFluors are not suitable for flow cytometry on permeabilized cells without extensive work and protocol modifications.

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Additional information can be found on BioLegend's and Thermo's websites, although this is more accurate for PFA fixation.