It depends on what type of work you will be doing and what type of trees you will be working on.
The most common tools I use on a reg basis are Wire Pliers(used when wiring and de-wiring, to tighten trees into the pot and guy wire), wire cutters and scissors. If I could do it over again and I might recommend to myself some inexpensive pliers from the hardware store, ARS scissors(should be around $20-30, made in Japan good quality steel used for cutting grapes) or Kaneshin scissors and then a Kaneshin med or large size wire cutter from ebay.
I'd also invest in some wet stones to sharpen my scissors. After this i'd start buying tools as needed. The two brands I have come to mostly buy are Kaneshin off ebay and Masakuni from California Bonsai Studio. You can't really gone wrong with either of these brands with masakuni generally being slightly higher quality and price.
Stainless steel usually does not rust while the black steel does rust, but I believe maintains an edge slightly longer. I usually go with non stainless, althought I might recommend Stainless for repotting tools as they get wet more often than non-stainless. Hope that helped.
