This depends upon the preference of yours.
If you want job then the best ug courses are
1.Chemistry:Huge industrial applications are there so many jobs are available.
2.Statistics : This is the most promising field in ug for jobs.You can go to Data science for jobs from here or you can go for an analysis job.
3.Mathematics:Applied maths like OR has broad industrial application
4.Economics:This is also one of the most promising course for jobs.
5.Engineering
Now if you want to research the best fields are
1.Mathematics
2.Statistics
3.Physics
4.Chemistry
5.Zoology -Botany