Best one period? M3 Perfect is what everyone crows for. However, good luck not paying triple digits for one, if you could even find one selling it. Unfortunately, its age would preclude that it might start having issues with any capacitors on it or some similar electronics issue not much longer.
About the only real cart being produced now is the EZ4. But as good as it is that Team EZ has been still actively supporting for firmware for the EZ4, it is distressing and disappointing that the ezclient they officially released is such garbage.