BTS serves a much greater role in the Bitshares blockchain than XRP serves in Ripple.
* Bitshares aims to be a profitable DAC, by burning more in transaction fees than the costs needed to sustain the network (paying witnesses and workers). The profit appears via burning BTS, reducing its supply and making each BTS more valuable. This is analogous to a company buying back its own shares (instead of issuing a dividend). Many investors prefer this system to a dividend, for example, Warren Buffet / Berkshire Hathaway.
- This functionality is similar to XRP in ripple, with the exception that the transaction fees are greater to actually try to profit, instead of burning only some negligible fraction of an XRP. Also, all of the BTS supply is now distributed, while the vast majority of the XRP supply is held by ripple labs, waiting to be dumped on people.
- This is also similar to ETH in Ethereum, which 'fuels' the running of its smart contracts.
* BTS also serves as collateral within the system to support smartcoins. Issuers of these smartcoins thus need to have BTS to support their projects, creating support for BTS.
-This functionality has no equivalent in Ripple or Ethereum.
Compared to both XRP and ETH, the supply/inflation situation of BTS is also far superior.
XRP: While there is no inflation of total supply, More than 80% of XRP are held by Ripple Labs to be sold over time. This actually represents a substantial future inflation.
ETH: Currently Proof of Work mining with extremely high 18% inflation rate. In the future this will change, at which point it will become a much better value.
BTS: Currently running about 2% inflation, paying DPoS delegates.
BTS supply is far more distributed that both ETH and XRP. It has a couple 3% whales but most are a lot smaller. XRP is mostly in the hands of one entity. ETH still has a lot of really large holders.