On those two models, manual switch
batteries are strongly recommended. [On some other models, e.g., Kr8 and 801, I prefer automatic, which is well implemented, whereas I do not like how their manual switches are implemented.]
The 510 and eGO manual switches work great and provide full control of the
vaping process (e.g., no primer puffs needed and no accidental firings due to noise or movement). I have read that the button on the 750 mAh Riva has a more pleasant touch than the eGO, but that shouldn't stop you from getting the 900 mAh Mega eGO battery or 1000 mAh Mega Tornado battery. [And for even higher mAh, consider the 1300 mAh Hello 016.]
I discuss all these "Fat Batt" models toward the bottom of
this page of my updated WWV illustrated guide. [NOTE: I have not used any of them myself, so other veterans may want to add their personal experience and recommendations.]