While looking through the finder use the depth of field preview feature of your camera, stopping down your until you get the effect you're after ..
I'd look at Zeiss primes .
Until you can answer that question yourself , don't buy anything .
Simple . Appeals of death sentences are far more costly than executions .
AND ....$ 35"00 per day for keeping a person in prison is laughably under actual cost. Cheaper to send him to Harvard.
In terms of cost , life without parole is less costly than the execution process,
And , " Thou shalt not kill " is a commandment to all of us .The good as well as the evil .
Thatt you need ask such a basic question suggests to me that it would be irresponsible of you to do the job considering your lack of experience and knowledge .
For best image quality ; a prime and zoom with your feet . The ultimate being Zeiss if you can afford it .
At shutter speeds of 1/40 Or 1/50th seconds blurrienessis is certain iwhen shooting flowers in the slightest wind . Image stabilization does nothing to steady subject matter so even a tripod would be of little use at such slow shutter speeds .
Try as a starter 1/1000th then briefer and briefer until you get what you want . Then too, so long a lens for a flower would not be my choice which would be closer to 100mm , prime macro , often with a strobe mounted on my lens or someone hand holding the strobe at f / stop of f/16 or 22 . The shutter speed then becomes the peak duration of the strobes burst of light which, depending on the power of the flash could be 1/20 thousandths of a second or less .
I suggest you try a prime 300 on a sturdy tripod for a comparison .
Then again , why 3 " So called " zooms " if you're most interested in a 300 ?
Like a carpenter saying his favorite tool is a rip saw .
I think that the decision as to which lens is the right one for the job should be based on the nature of the job.
Do you consider your reply an answer to the question ?