"Realistic" is understood but overall subjective.
My suggestion is to try a few text to speech converters using free trials or just simply free apps.
Decide what you like with respect to features, functions, user friendliness, and, of course, realism/realistic.
Probable that you will need to make trade-offs. In general, the more realistic, the more expensive.
Set up a block of test text of what ever length and nature you desire.
Then run that text through the converters. Test options, voices, etc..
Pick the converter that is most realistic to you.