hi im male and im 14 i am wondering what is the best thig to use for anal penetration?

The BEST thing is a toy manufactured and designed for this express purpose.

There are silicone dildos with flared base on the market. The flared base is essential so that it does go "all the way in" by accident, requiring a rush trip to the emergency room.

 Remember anal is not for everyone. You may decide that you don't like it.  Be sure to us plenty of water based lube if you decide to try it.

well if your trying it out for your first time then alot of lub on your finger(s). Its better to see how it feels then to stick something to big and rip your anus... yah its possible if you go from super tight to super big. start off by inserting just the tip of the nail and then slowly work your way up... LUB IS A MUST