The curves of the letters are not smooth.
Converted to curves:
When exporting to jpeg, tiff, etc., this problem is quite unpleasant.
Both the images in your post look almost identical, possible due to saving them in a very low resolution and further degraded as this forum resizes the images to fit. Please post a higher quality of image or upload to a free online file storage and provide us links to them. It would help us help you better.
The one image certainly looks a lot better than the other (converted to curves) I believe. Is antialiasing on? What resolution is used?
The image is not resized. Both at 300dpi and 600dpi is the same. For screenshots is increased 350%. Font is PF Agora Serif Pro Medium.
This is a screenshot. 300 dpi
at 350% the jaggies are going to really show what does it look like at 100%? I suggest you post the 100% on a test web site and look at it.