Still the old Giant Defy?

I'm not certain I'd spring for expensive wheels for that. But tires themselves can make a great difference in how a bike feels to you. Particularly how well it rolls. So if you aren't using a really good tire, that might be a very worthwhile investment. Better and more expensive tires both roll better with less muscle needed and also ride more comfortably. Flat protection is less in them, but if you aren't riding in goat head filled areas, then you likely can run really good tires and not flat very often at all. I use the tubed version of the GP5000 tires and while they aren't the best of the easy rolling tires, they aren't the worst by far. And they don't flat easy for me. I've worn out the last three tires to the point that if it wasn't for the tube, I'd be able to see the air inside them. No flats till then.