I'm currently in TCA and LCCA. As mentioned in previous posts, they each offer different benefits and have slightly different objectives. Here are some observations based on my experience as a member of one or the other for over 25 years, in no particular order.
York is unlike anything else - I drive several hundred miles each way twice a year to attend - but there's a lot more to TCA. TCA maintains an excellent museum and library; these are tremendous assets, and IMO everyone who cares about preserving and disseminating the history of toy trains should support these assets.
TCA used to be rather arrogant, and many members were focused only on making money and acquiring trains. LCCA has been less so, and this aspect of TCA has softened considerably over the past 5-10 years.
You'll probably find more operators in LCCA than TCA, but TCA is paying more attention to operators in recent years.
Both organizations have good printed materials. TCA's magazine has far more information about about prewar trains than LCCA's.
LCCA seems to be more effective in trying to get kids interested in toy trains. IMO, LCCA is more responsive to its members; TCA can sometimes be more of an "old boys" club.
LCCA is very Lionel-centric, especially after merging with the Lionel Railroader club, to the exclusion of other manufacturers. The relationship seems a little bit too chummy, which bothers me. TCA appears to try to give equal time to all manufacturers.
LCCA's convention cars have more subtle club markings. I like that, but others might prefer markings that more obviously identify a car as a club convention item.
Another consideration is meets in your area - who has more?
If I had to pick one, I'd pick TCA because I feel an obligation to support the museum and archives for a hobby I love.
Hang around long enough, and the TCA haters will come out.