eXRD vs XRD
You may be confused as to why there are two different tokens for Radix, but don't worry!
eXRD is the Ethereum wrapped version of XRD, launched in 2020 to increase distribution prior to mainnet launch. eXRD can be held in any Ethereum compatible wallet and can be bought at KuCoin, gate.io, UniSwap and others.
XRD is the Radix network native token, launched in July 2021, required to pay transaction fees in the Radix network and earn staking rewards. It can be bought directly only at Bitfinex at this moment.
eXRD is swappable 1:1 for XRD, using Instabridge.io or Bitfinex. Through Bitfinex you can swap both ways.
Instabridge requires an instapass.io KYC verified account. Bitfinex doesn't require KYC for the swap.
Supply is 9.6B (XRD + eXRD is what counts) + 2.4B (locked XRD for stablecoin project) + 300mil/year XRD emissions (to pay nodes and staking rewards).
As they are swappable 1:1, arbitrage should keep the price differences between both assets small and short lived.
Which one should I buy?
Buying XRD is the better choice since you can stake it and earn rewards. You could buy eXRD and swap it to XRD but you either need Bitfinex or Instabridge (which uses Ethereum gas fees and needs KYC on Instapass).