i had the same debate with myself a few weeks ago. i was really leaning toward the Riva. Then after thinking further and reflecting on a year of happy joye 510 use, i figured i'd go with the name that i knew. i spent a few more bucks on the eGo and i don't care... i love that thing!!! i wish i'd have gotten it sooner. now, as much as i'm praising the eGo, there will be others that will do the same for the Riva.
i guess my answer to your question is... you're on the right track either way. they're both excellent PVs.