I am pretty new to vaping as well and I also got the Riva 510. I can't really compare it anything else as it is the only device I have but, it seems pretty awesome to me. I've had mine a little over a month now and haven't had any issues with the device. All the atties that came with it and the one LR atty I bought all still work very well too.
As for flavors, as someone who smoked Camels and thought I would like the tobacco flavor, I ordered three and didn't care much for any of them. I got the Menthol Blend, RY4, and Home Countries. Home Countries was the best to me out of the three. Oddly I only ordered one non tobacco flavor and that was coconut and it was the one that turned out to be my favorite. Speaking of which I need to order some more lol. Anyone one who has tried mine at work, they all seem to like the coconut too, the best.
Other then that, I would recommend getting a drip tip, they are cheap and can be used on the regular atties that come with the Rivas. However, I do recommend getting at least one LR atty, I found I got better flavor while dripping with these and better TH and VP. Might want to try out the boge cartomizers too, I found I really disliked the carts that came with the kit and even disliked the smart carts I ordered too.
Good luck!