For multiple trips, within a period of two months, the country with the longest length of stay should be taken as the main destination (Article 5(1)(b) Visa Code):
if the visit includes more than one destination, or if several separate visits are to be carried out within a period of two months, the Member State whose territory constitutes the main destination of the visit(s) in terms of the length of stay, counted in days, or the purpose of stay; or
If one event is longer than the other, then that is the one you should select.
If they are both the same, then the country where your will first enter the Schengen Area (Article 5(1)(c) Visa Code):
if no main destination can be determined, the Member State whose external border the applicant intends to cross in order to enter the territory of the Member States.
The length of stay is based on what is known at the time of application (i.e. any later changes doesn't matter).
Note: The Visa Code quotes are based on the 2020-02-02 text.