Why should I use these towers?

I’ve played this game a decent amount but I’ve never really tried very hard if that makes sense? A ton of my time is just having fun with my friend so we sorta stick to the same few towers. I’ve never seen the appeal of gunner, mortar, engineer, or beast handler. Are they any good? I’ve been seeing a ton of people talking about the mortar on this subreddit so I was wondering.