In terms of the CPU, here's where they stand.
The Tegra 3 utilizes a quad-core Cortex A9 setup. Cortex A9 delivers 2.5 DMIPS/clock in raw performance (which can be hindered by slow ram, limited cache, etc.). At 1.5ghz, that is 3,750 DMIPS/core for a max theoretical of 15,000.
The MediaTek MTK 6589 utilizes a quad-core Cortex A7 setup. This delivers 1.9 DMIPS/clock. At 1.2ghz, that comes out to 2,280 DMIPS/core, or 9,120 theoretical max.
That means that the Tegra 3 has a CPU that is up to 65% (rounded up) faster than the MTK 6589. However, the MTK has much better power consumption. Which is more important to you, performance or power usage? (Tegra 3 uses a companion core, but its power savings isn't huge). The MTK is literally the lower-powered quad-core found in the Exynos 5 Octa.
As for the GPUs, I'm not an expert there, so I can only point you to the 3D Mark reference page (which is one of the more accurate GPU related benchmarks on Android right now).
Best Mobile Devices July - 2013
The top scoring Tegra 3 device scored a 3,204.
The top scoring PowerVR SGX544 (non-OCed, paired with a 1.2ghz quad A7) scored a 3,154.
What does this mean? In gaming situations, I would expect both devices to perform similarly. In CPU-related tasks, the Tegra 3 will be up to 65% faster. All around, the MediaTek will offer better battery life.
Ask yourself, which phone offers the best software for your needs? Possibility of official updates? Custom ROMs, if that's your thing?