Should I get Minecraft or the Forest?

I would get Minecraft now because it's a lot of fun and the Forrest is in Alpha still so it's really buggy and really annoying to play right now. I would suggest getting the Forrest after it has been updated a lot more.

I have heard the forest is a good game. I have never been able to get into minecraft, so the forest it is! Also, the forest requires a fairy hefty computer to run at decent settings.

In MineCraft, you can build stuff. It also kinda teaches how to survive, you can build a mansion if you wanted too! So, you should get MineCraft.

I would recommend Minecraft.

Some people frown upon it as childish, but hey, there are tens of millions of downloads already so lots of people definitely play it.

It keeps you occupied for long amounts of time and is a very good time killer.

It has gotten me extra credit in a number of my classes through building historic scenes, things from books, and models of cells.

Its overall really fun and a great feeling when you look at something amazing you've built.

I might give a bit of a biased answer, seeing I've played Minecraft but not the forest. The final choice is yours.

I suggest you go for Minecraft, the PC Version mainly. The reason is a large variety of reasons.
Minecraft supports modding(there's even a community that makes insanely awesome to really weird mods).
There's also ideas of: doing a Survivor man style play, Going into Creative Mode and create/replicate nearly any building/structure/vehicle(large scale)/character(large scale), Playing/Creating a Survival or Adventure Map… There's also the "Parkour" Maps.
There's Options of Playing/Making PVP maps, but only if playing on server worlds.
People also have made Minecraft "Machinima" videos of a story line, well that and the Yogscast also had a story line that's been on Ice (Shadow of Israphel).

There's also options of mixing the options, like mixing Mods with Building things, making a Modded PVP map if you have friends that can play on Minecraft servers. Or if you're wanting to try a chance of making an Adventure Map with RPG elements(SethBling on Youtube points stuff like this out.), then have your friends try and beat it.