I prefer offsets for Seneca. Something like a set of DMM Peenuts works well. You could also get some of the larger brass offsets (maybe sizes 3-6) if you don't mind spending money. To be honest, though, I never place many micronuts at Seneca.
You'll definitely want micronuts for many of the 5.10 and up routes at seneca -- especially faces. Never really placed any offsets myself, but there is certainly opportunity to do so. A good selection of standard brassies should do you well.