It comes down to preference, as far as TMobile bloat you should have got the US unlocked S20+ which is a cleaner Samsung experience phone as intended by Samsung instead of the crappy carrier models with all the carrier bloat/customization (sure you can disable).
As far as which is better, I have used both and most of the time I have a Pixel, iPhone and Samsung phone. S20+ is definitely more premium feel and feature rich, better battery life etc. 4 XL is great as well if you prefer Google experience and fast platform updates. It's honestly a very sensitive topic and people fight over arguing one is better than another. But that's something only you can decide on what you like. All I can say is they are both flagship phones with different priorities and experiences. If you plan to keep your phones long then I would wait few more months for Pixel 5 instead of buying 4 XL. If you change phones often then try out the 4 XL and you can switch to Pixel 5 later. Do note that trade in values are not great from Google so if you buy 4 XL now and switch to Pixel 5, plan on selling the phone yourselves for better value.
I'm personally trading the 4 XL for the US unlocked Note 20 Ultra since Samsung is going to give crazy trade in value for my Pixel 4 XL ($650 most likely), anyway I'm going to get the Pixel 5 in few months. I'm also contemplating on temporarily getting the 4a until Pixel 5, if I need a pixel until Pixel 5.