I am long nat gas through the ETN "GAZ". There is definitely a tremendous more upside potential in nat gas vs the downside risk. However, you need to be able to withstand some more downside vol at least until some of the supply lines start to drawdown, which may not be until winter here in the Northeast.
Regarding DBA, soybeans have had a run, corn is out of gas, sugar is at 28 year highs. Only wheat, which is hitting some support levels, has upside potential. IMO.
Also for UNG, GAZ, and a few other ETFs, you are going to pay a premium over NAV for the reasons mentioned earlier re: CFTC spec limits.