DISCLAIMER: I have never played in ESEA, CEVO, IGL, or ETF2L.
First, let's temporarily ignore the Bitcoin/Malware fiasco.
STAYING WITH ESEA
This is the easy option. The community does not have to undergo the very intensive and risky process of switching leagues. This option gives us what we already have: ESEA stats, ESEA servers, ESEA admins, ESEA website/content, ESEA LAN, ESEA prizes, and ESEA client. Whether these are good or bad for us is relative to other leagues and is going to primarily be a matter of subjective opinion, but will have objective results.
Choosing this option should make us expect more of the same. These things (and therefore the quality of ESEA) could change, but we should not expect it (again, Bitcoin/Malware incident not included for now).
CHANGING LEAGUES
This is the difficult option. It takes a lot of work to successfully transfer leagues, and it takes effort to accommodate the players. Choosing the league(s) presents us with multiple options, the most prominent being CEVO, UGC, and ETF2L. All of these options have pros and cons that were briefly examined in this thread. None of these options are currently objectively better than ESEA, and will most likely require changes to accommodate the new playerbase, which are factors that make this option risky regarding the future of NA TF2, no matter which league(s) we choose.
The good news is that it seems CEVO/ETF2L/UGC are willing to work with us, and this means these leagues could potentially be better than ESEA. What these leagues lack in comparison to ESEA (including LAN and competition) comes down to resources and establishment. It is possible for these leagues to eventually offer everything ESEA has and more, but will they? How much time, money, and effort will it take, and if and when it is accomplished, will it have been worth the possible negative consequences to the NA TF2 scene in the meanwhile?
BITCOIN MINING AND MALWARE
The other side of this story that I have ignored so far is the aforementioned Bitcoin/Malware incident concerning the ESEA client. We should seriously consider whether or not ESEA will continue abusing its customers through its client, such as it has done with mining bitcoins and failing to completely uninstall. Right now, there is no clear evidence that the client's complete access to your computer was used maliciously other than to mine for Bitcoins, but we should consider if such a thing is even possible, and if it is, whether or not ESEA is likely to do so.