This is a tricky question to answer. In the 5wt and over class, it's tempting to go with my first rod, a 10ft 7wt Shakespeare Expedition. It was a lovely rod to cast and a fair bit of sentimental value. But then I have a Helios 2 9ft 5wt that is lovely to use, so versatile, and has been used so much that numerous memorable fish and adventures are attached to that rod. It's tough to choose between the two. On top of that, in Uist last month, a 9.5ft 6wt Vision Stifu I picked up earlier in the year was the perfect tool for two windy days, which produced the best fishing of the week.
On the 4wt and under class, it is difficult for similar reasons but also situational. I have a 10ft 4wt rod built on a Taniwha blank, which has been my go-to loch and boat rod for the last few years; it is a brilliant fishing tool. It has also served well as a dry fly rod on the Deveron. Recently used its 3wt counterpart for a few days boat fishing and will be doing that again. But I also have one of Sandy's McFarland Spruce Creek 693 rods, which is sublime. But I doubt a boat partner would thank me for using it in a boat.
No, I am too much of a tackle tart to pick just two favourite rods. I need and want them all