I’m looking for a Serif font for h1 title which will pair well with Lato 300,400
There is no specific rule for the combination of text fonts, what I would recommend is to do trial and error experiments. The idea is to find a harmony and that is pleasing to the eyes and help reading with a good spacing and size appropriate text, separation, line h etc
I’m not helping, I know, I apologize for that.
Good luck I’m sure you’ll find the right combination, yourself.
Like TexTheme already mentioned it is important to find a good harmony between fonts and always take care readability comes first.
In addition to what was already mentioned by TexTheme, if you need inspiration or a pointer in the right direction here is a tool I use sometimes: Type Genius
Just type in Lato in the field and they will give you suggested fonts which do well in combination with Lato.
Hope this helps you.
That website is exactly what I was looking for, Thanks