I've never used infernape myself, and have only just started using lucario. You definitely want alot of type coverage, and as you say, you don't want 3 pokes with the same weakness. Since you have zapdos with heat wave, infernape's fire moves aren't as critical, but still useful if your zapdos is taken out. Im by no means an expert at this, only started recently, but if you are missing out on dark/ice moves in your team then probably pick lucario, and if you need the grass/sweeping power of infernape go with that.