i am exploring similar at the moment. Generally a seperate system will always sound better, but can cost more at the lower price range due to needing amp/receiver (though second hand can help this).
I think the most important question would be how much space you have and do you have the space for separates or not. You can get wall mounted options to give the front 3 speakers in a tidy configuration, but this may not be acceptable.
Overall TV speakers are poor, they use small drivers with a low total power output. The focus is design and thin bezels and screen quality rather than sound quality. Nearly any sound bar will have a significant improvement, so they aren’t bad. All depends how much you want to spend, space available and how visible your speakers can be.