ideal titre volume?

Why is the most ideal titre volume between 25 cm³ and 50cm³ if using a 50cm³ burette?

less than 25cm3 and any absolute measurement error becomes a larger percentage error.
eg if you have a titre of 1cm3 and an error of 0.1 cm3 this amounts to a 10% error in the final result
if you have a titre of 25cm3 this amounts to an error of 0.1/25 x100% = 0.4%

If you have titres greater than 50cm3 you have to refill the burette introducing more errors and more possibilities for inaccuracies.