There is no absolute correct answer to this dilemma.
Is the A320 operator a place where you would be happy spending most of your career?
If so, take a position if offered, especially if it is an airline where progression is governed by seniority.
If it is not a long term choice, will it help you get a job with a carrier where you would like to stay? Probably.
The cost of A320 Training is probably similar to the upgrade training on the ATR, which you will probably have to repay if you want leave within 2-3 years.
I understand the advice to take Command but it is of less value in f you intend moving to an airline where entry is at FO level only.