the main differences I see between Tau and Ether are marketing and liquidity
Marketing
All the cryptocommunity know about Ether but only a few about TAU
Liquidity
Ethereum is on Polo, Kraken, Bitfinex, btc-e, GDAX, Yunbi, Bittrex, BitMex, Gemini, Yobit, Cex.io + 10 or more
AGRS is on Bittrex
My ideas:
Marketing
More interviews explaining how TAU is security (Turing completeness) and expressability (The new Tau language) (correct if this is not true)
If you believe in Turing complete: Ethereum
If you believe in Turing completeness: Tau
If you're not sure: Diversify in both
Liquidity
Explain more exchanges the project and why they should add TAU