Note: I have nothing against either game I speak negatively about, nor do I think one is better or more superior. What i'm going to talk about is all based on opinion.
So, this is a small debate that i've seen thrown around the internet time and time again, and I honestly have found myself in certain arguments when it comes to this game. Some things I've read however are just completely out of whack, like "oh, Terraria is just a cheap knock off of Minecraft", or "it's just Minecraft but as a side scroller". Believe it or not, I actually used to think the same thing, but as time went on, both games got updated and more playable, and I came to realize that both games have their faults and positivies that make them their own individual games respectably.
To start things off, I started playing Minecraft back in it's alpha days, or as some people like to call it, "the simpler times." That's not exactly false. Back when Minecraft first started, it was very easy to get into and a lot of fun. You break down trees, you build a crappy house, and you get killed by mobs because you weren't prepared. Unfortunately, if you try to get into Minecraft today, it's a bit more difficult. I wouldn't say it's necessarily impossible, but if you were to jump into Minecraft right now, you'd probably find yourself getting screwed over much quicker than you would when it was in it's alpha stages, at least that's how I feel about it. Some of the updates that would make this happen would be the updates that effect the mobs specifically. They've made it to a point where the mobs are almost impossible to kill under certain circumstances. For example, if you're swimming in water and you see a skeleton, just kiss your items goodbye, because the skeletons now have a much smarter AI that'll make them shoot you over and over again to put you into your grave quick. Zombies are the same thing, when it's daytime, they now know to hide under a tree to get out of the sun so they don't die. Basically you could be running into a sea of trees, and all of a sudden, a zombie comes out and inflicts damage because it didn't burn away like they used to. Granted, I like difficulty in games, and Minecraft is definitely at a point where it is pretty difficult unless you play on peaceful, but I fear that it's getting to a point where the updates are kind of taking away from the original intention of the game. I know that naturally games are supposed to evolve, but with the way Minecraft has evolved, I just don't get as much enjoyment out of it. Of course, there are mods to fix that problem, and trust me, mods make this game a lot of fun.
Onto Terraria. Now, i'm probably a little biased because over the last 2-3 days, i've ranked up about 10 more playing hours into this game. I used to play this game all the time before I sort of got bored with it and left it to collect dust for a while. But, a friend of mine mentioned to me that they've been releasing updates for the game that make it much more playable than it used to be. I started playing it again on Friday night after hearing that and i'll tell you that unlike Minecraft, the updates to this game have made it so much more fun. The main difference between Minecraft and Terraria is the fact that in Terraria, the main concept is spelunking. You try to get as deep as you can while finding ores and materials along the way to make better equipment and to fight off bosses and bad guys. You do have to be a lot more careful in this game than you would in Minecraft because if you break one block without realizing there's an empty space below, you can find yourself dying quite quickly. The same thing can happen in Minecraft as well, especially when you're doing some blind mining just to look for a cavern or ores. I would say that the one thing Minecraft does have over Terraria is that when you die, you lose your items unless you have a mod that takes that away. In Terraria, when you die, you don't lose your items. Part of me wants to say that it kind of makes the game a little bit less scary because death isn't something you're too worried about. However, in it's defense, Terraria is a spelunking / cave exploring kind of game. I would much rather have my mind set on exploring a huge cave instead of having my mind on whether or not my next block removal will kill me thus losing my items. It definitely makes the game more enjoyable when you're not worried about losing your items.
Both games have their flaws, and both games have their strengths. If you were to come up to me now and ask me which one I would prefer to keep on an island, I'd probably have to go with Terraria. Unfortunately with Minecraft, I've found myself getting bored of it really quickly. Some of the things you can do in Minecraft seem to be all based on luck and you have to be able to find certain things at the right time, or you'll find yourself just sitting around waiting for said events to happen. With Terraria, there's a constant evolution going on, where if you keep moving, more things will come your way. You find more items, you find more weapons, and it's just a great way to spend 5 hours of your day, and being on an island by myself, i'd need to be able to waste my time until the sea washes me away and I die forever. I may have lost my life, but my Terraria world will live on for centuries. Again, both games are great for their own reasons, but Terraria is just a lot more fun and exciting.