Seeing as there is no solution on the horizon for the congestion on the Bitcoin network, I want to diversify my portfolio into some crypto currencies that are more scalable. I wonder which altcoins have the highest transaction capacity. I also wonder how Ethereum and Dash specifically would do if they had the number of transactions that bitcoin has x 10.
You probably want to look at more factors than block size handling. For example, Bitcoin in theory could handle millions more users easily if the Lightning Network was successfully rolled out. I actually think Litecoin may rise on the capacity issue. Litecoin is pretty much exactly Bitcoin, but with built-in 4 times more on-chain capacity, because blocks are 4 times faster. Litecoin devs have committed to follow Bitcoin's development too, which means implementing SegWit, which provides up to another 4X capacity. Then if you add in Lightning Network and other scaling technologies on top you really have a lot of capacity on a very old and established coin, which is probably the fairest launched and best distributed coin (including better initial distribution than Bitcoin).