I don't buy ETFs and plan to hold for a long time as there is the contango effect and holding costs to consider but there are quite a few trading angles around to keep me busy.
Contango is an issue for ETF and ETC that have to purchase futures contracts, and as a result contango and backwardisation risk can be significant issues to consider when holding for medium to long term periods. There are many that do not buy futures contracts and simply buy stocks within specific sectors or to replicate index performance.
My rules to hold ETFs for the long term
1) they are non leveraged, so that performance can be measured against an index more accurately without options/swaps/futures instruments affecting performance.
2) they have low fees(preferably below 1% annually)
3) they are liquid enough to survive massive inflows/outflows when markets become volatile.
4) try to stick to the simply structured ETFs that have investment approaches that you can understand.
Choosing more complex ETFs should be for more experienced market participants, there are lots of options out there, but really just a handful of well picked ETFs and some decent market timing is all you need IMO.
