Destiny and Triumph are essentially sister ships. They were the first !00,000 ton ships in the Carnival fleet. Rooms are large by industry standards and they even have showers you can bend over in. Nice pool areas, public rooms and good entertainment venues.
I would personally prefer to sail from Miami , not San Juan. Just a travel preference.
San Juan is an interesting port and I enjoy the Old San Juan area which is only blocks from the pier. Great shopping and history, gambling if you like it, restaurants and clubs if you are there late enough. St Martin and St Thomas are both great stops for shopping and also great stops for beaches and water activities.
The other cruise offers a nice mix of shopping ports, water sports ports and maybe a taste of something different in the rain forests of Dominica.
I'd say you can't miss with either itinerary or ship.