Ethereum of course. It's a NO brainer to use it as it's the second most easiest to trade for fiat or alts. Better use ethereum sooner rather than later.
Add 'Burst' and '0penBazaar' will BLOW UP! lol But yes I believe 'Burst' will be a wonderful addition as it's gaining more popularity and having 'Burst' as a payment option @0penBazaar will bring more people into 'Burst'. This is a genius idea by the way. Alt's on the rise ;)
Yes - xmr
This is fantastic. I love to see dogecoin available here. There is a huge community behind dogecoin.
Monero
Steem and Gridcoin perhaps? I like Gridcoin... And Steem.
BTS → bitUSD, bitCNY, bitEUR STEEM →STEEM DOLLARS
How about DogeCoin? has the lowest transaction fee among BTC based coins with 1 min transaction time.
All currencies. Add 'em all!
Seriously, Amazon and Ebay take all sorts of credit card and paypals, let's have the best marketplace up them by having even more choices with users who could all use a market we could share items even if we don't share the coins we like.