The first one has no blending done to it..
The second one is blended, but it's low quality.. also you could have blended the colors even more
1st pic: no flow. no blending.
2nd pic: needs moar colors. and moar quality.
Thanks for the comments
How could I change some things in order to fix or improve the things you both mentioned?
How could I blend the first one better for example?
Gradient maps
Photo filters
Depth
Lighting
All sort of things. Right now it looks like you whored some stuff for a BG then put some stuff on top of the render. In most cases that's what a signature is if you take out the adjustment layers and such but try and erase things and make it look like things belong.
The second one is sorta bland but the first is good you just need to blend it more..