The biggest model I've painted for my army and a nice centerpiece, the Trygon prime. I've had it assembled for more than 6 months now and since building it, I was blown away by the detail and size of the model. That size and detail meant an equally large paint job, but after a couple months of sporadic work and a couple weeks of more focused work, I'm happy with the result.
The other pictured models were done previously, they are just a good indicator of size, the Trygon stands almost 6 inches tall!