Tailwag, as well as considering which factors to use you should look closely at how these factors are applied.

Most mechanical systems use benchmark rules like 'horse must have a 40% win strike rate'. What sounds like a good logical rule falls down in practice in that it doesn't properly evaluate a horse's strike rate relative to other horses in this race.
e.g. in race A one horse might have a 40% strike rate and next best might be 10% yet in race B the same 40% horse might be opposed by five other runners with strike rates of 39%.

Of course in this instance you also have the problem that strike rate is not necessarily a good measure of current form or ability.

wunfluova