Good steaks should need no tenderizer, just salt and pepper.
However, if you don't have such good steaks, I would recommend a meat hammer (metal with spikey face). The steak hammer, using the coarse end, will break up the meat fibers. The fine end is generally used for pounding veal.
I haven't seen a chemical tenderizer yet that can salvage a bad cut of steak.
What seems to be the problem? Preparation can have a big impact as well...
