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The most contribution is the Research Points, which can only be paid in time... (by claiming daily)...

Those are the most valuable over time...

Parallel to that, is donating PART/SHARD to the guild for Guild upgrades... but those are quite costly... and if whenever anyone leaves the guild, 50% of that is retained to the user that donated. The guild looses it all.

Keeping the maximum players of a guild claiming daily, is probably the best strategy in my view, for any guilds. Researched stuff is super valuable long term.

Thanks for the explanation :-)