It's torch or flowing lava > lit furnace > stationary lava > burning netherrack. The last one produces 6 mB/s (4 cobblestone per bucket of lava) while requiring a cobblestone block per 42 seconds.. Pair two of them with one of TE3's Magmatic Dynamo, which under full work (80 RF/t, or 1600 RF/s) uses 8.888... mB/s of lava and you have free energy and some spare lava. An Igneous Extruder generates one cobblestone per 2 seconds, so it's enough to drive 10 such generators, for 800 RF/t.