Get everything, on both offense and defense, built at level 1 for bonus buildings. Otherwise:
for defense, healing tower, panic manor, shrines (dark>light imo), and tactics room are the best. Healing tower is probably the most important one.
for offense, after escape ladder is by far the best, followed by healing tower and bolt tower. Panic manor is alright I guess.
Basically, priority is everything at level 1>escape ladder o>healing tower d>everything else listed above.
In general, defense structures are better than offense structures. How useful a defense structure is, except for healing tower, is ultimately dependent on the map you face. Your defense, however, is a constant. Like panic manor can be good, but if the team doesn't use visible buffs (common because Aversa is a thing), then it's just a waste of space. Also, and counterinutiveily, there's validity in only use three or four buildings: it gives you more space, especially for smite plays. I only ever use four buildings at a time (healing tower/ladder or bolt tower/fortress/bonus) because I find the space more valuable. On defense, however, you always want to use as many buildings as you can.