They're both shitcoins, so I'd advise not buying either one. I'm not real familiar with xvg but rdd is total garbage. You might get lucky if someone decides to use it in a pump and dump scheme, but I'd sell it as soon as it pops. If you hold either one long-term, you're asking for trouble. Rdd just went up to something like 160 sat, but there's no support because no one uses it, and that's not going to change.
This. RDD has lost it's way. It occasionally gets pumped by pumper-dumpers who accumulate cheaply, but it always falls back because no-one uses it.