All cats are going to have their own personalities/preferences that you'll just have to observe and work out. But probably the most universally loved cat toys are going to be empty cardboard boxes. Put a couple different sized ones around the house and swap them out for different ones every few weeks. They'll usually love that more than any toy you can buy them.

The wand toys like this: https://www.jacksongalaxy.com/collections/toys/products/da-bird-collapsible-wand-toy-by-go-cat are great for kittens with excess energy. As are these: https://smartykat.com/products/instincts-soarin-squirrel-happynip-launch-cat-toy/ Jackson Galaxy and Smartykat are both brands my cats love.

As far as cat trees go; I saved and bought a huge floor to ceiling one. The cats went nuts on it, for about 2 weeks, now they couldn't care less about it. So your mileage may vary.