Derailleur or shifters?

[Simpsonna]

I have a Shimano Alivo Rear Der. and some kind of shifters (See photo) They came stock with my Trek 4300 a year ago. They're the last few things I haven't upgraded.

I'm no expert mechanic but I am decent with adjusting the shifting and I cannot get it just right. If I can get the bottom four gears to shift right the top for are a little screwy and vice versa. Both the shifters and the Der have taking a beating form me and I'm sure they need replacing.

P.S. The hanger is fine, amazingly.

My question is would this be mostly caused by the Der. or the shifters? I'm a college kid so I'm very tight on cash but I will only buy close to the top of the line. Which means I can only really afford one right now. Which would make the most difference?

[J-Dubs]

Shifters are a better investment.

[DownCycles_Stef]

Make sure to check the B-Tension screw before you get do anything else. It's probably one of the most forgotten adjustments on a bike. On a Shimano derailleur, the upper pulley wheel of the derailleur should be as close as possible to the cassette when in the lowest (biggest size) rear gear, on SRAM derailleurs it should be about 3-5mm away.