The summoner storyline is my favourite, of course. But then, I'm biased, because it is Lyland's main job.

It does go beyond mere bias, though. Primarily, I was thrilled by the summoner's close links to the main storyline in ARR. Given that it's one of the Scions' main goals to defeat primals, it makes sense that their ace would be someone who's specifically trained to destroy primals by tapping their aetheric essence. And the summoner storyline remains the only one I'm aware of that specifically features the Ascians, the prime antagonists of the main storyline. And that makes it seem even more likely to me that the summoner was "meant" to be the canonical class of the game (at least for ARR; it's hard to deny that the dragoon has taken over as the "iconic" job in Heavensward).

And then there's the Allagan connection, with summoners being the ancient civilisation's precursor to the Ultima Weapon. In my imagination, going into the Crystal Tower and the Coils of Bahamut had been both a thrilling and sobering experience for Lyland, as he gradually learnt that this ancient art which he thought would be a force for good actually had tainted roots. The turn of events had a powerful, far-reaching impact on his character development, that continued into Heavensward.

And finally, taking on Odin in Urth's Font was that much more meaningful as a summoner armed with a fully awakened Veil of Wiyu. It felt right, in that Lyland was avenging Wiyu, who gave her life to prevent the Elder Primal from killing her comrades, some 5,000 years ago.

TL;DR version: Summoner for life!