In any generation of Roku devices, there's always a "top of the line" device that works better than the others. Other devices in any generation may work well, but one is always considered the best, usually by the processor, the onboard RAM, the video, or other features. But there's always one top dog.
You didn't say which Roku you have, so we're shooting in the dark here. Note that if you don't have any of the devices I'm about the list, then understand that you'll likely get an improvement if you got a different device at the time you got yours, meaning yes, you would get an improvement today.
In the early years, there was one device in 2008. In 2009, the Roku XD-HR was top of the line, then in 2010, the Roku XDS was top dog.
That spot then went to Roku 2 XS in 2011, before the introduction of the Roku 3 in 2013. Hardware issues kept the Roku 4 from being considered the best in 2015, which most picing the updated Roku 3 as best device to get.
In 2016 came the Ultra. That model name has been updated a few times, and the Ultra remains the top device today.
Today's low end devices perform on par with the Roku 3 in responsiveness, if not a little better. And to long time Roku users, that's saying something, as the Roku 3 was beloved by many.
As for which is the best to get, the simple answer is to get the top of the line device. However, depending on which features are important to you, a cheaper device may be the best choice for you. Many users are high on the Roku Express 4K+ (model 3941). I have no personal experience with it.
Ultra is top of the line? It might be the most expensive but the Ultra is defective. We are on our second unit and this one has also failed. Roku support has hung us out to dry even though we are still in the warranty period. Support doesn't have a clue what they are doing, at least now. They seem to have gone downhill very fast in the last few months. It's time for a different brand! They have severely upset me with their ineptitude and failure to perform for me as a customer.
Nah it's not worth the aggravation. The ultra is going in the trash once I get something to replace it. I most certainly am not paying to ship it back as that would be throwing money away just to receive another defective unit and I would have to buy something to use in the meantime anyway. First time they sent me the replacement up front and now they won't even communicate with me. I'm done. Roku as a company really sucks.