You are looking at two different reactions mechanisms (SN1 and SN2) and two different transition states now. That's fine, but be sure you are aware that this is what you are doing.
Imagine a primary alkyl halide going through an SN2 reaction. Your transition state, which will have a higher energy than your starting materials, has your reactive center associated with both the halide and your nucleophile.
Now imagine the same primary alkyl halide going through an SN1 reaction. Your transition state, still with a higher energy than your starting materials, has a reactive center which is not associated with either the halide or the nucleophile, and is positively charged.
Got those points drawn out in your head (or on paper)?
Good. Now imagine bulking up your halide - going up to secondary or tertiary alkyl halides, or even just putting a lot of substitutions in the alpha positions. You won't be changing the energy of your starting material much, but for the SN2 reaction, it will take a lot more energy to get the intermediate associated with both the halide and the nucleophile due to the size of the groups you have to push aside. The energy of your transition state will rise considerably. On the other hand, for the SN1 reaction, all those extra alkyl substituents on the reaction center will stabilize the carbocation, lowering the energy of that intermediate.
At some point the SN1 intermediate has lower energy than the SN2 intermediate, and substitutions take place by the SN1 mechanism instead of the SN2 mechanism.