What's the best option for better Jaw definition: Jaw or chin implant, sliding genioplasty, facelift/Venlay dentistry? (Photos)

Thanks for your question, its always difficult to know what is best, but you have great photos for this. Personally, i tend to like chin implants as they are easy, quick, effective and easy to remove if need be. also, you can shape them as needed by the patient. James Bonaparte

In my opinion your jawline shape is actually quite good.  Your best advice always will come form someone who can examine you in person, so I would take the advice of the dentist seriously.

Hello and thank you for your question. Based on your
photograph, a chin implant can be performed for
improved jaw line contour.  I always use a medpor implant with screw
fixation, which stays in place over time.  A silicone chin implant has a
high rate of malrotation over time.  Make
sure you specifically look at before and after pictures of real patients
who have had this surgery performed by your surgeon and not just a computer
animation system. The most important aspect is to find a
surgeon you are comfortable with. I recommend that you seek consultation with a
qualified board-certified plastic surgeon who can evaluate you in person.
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

When  considering facial rejuvenation to achieve a more contoured chin and neck line it's important to consider the anatomic asymmetry or deficit which is focal to your concerns.  When searching for your ideal self it is important to be honest with yourself about the degree of deformity which you are hoping to achieve and the amount of effort or financial cost it will take to achieve your desired goals. Look for a  plastic Surgeon who is board certified and can show you before and after photos of your desired results. 

It is difficult to give you options without seeing your teeth and occlusion (how teeth come together).  Even though your teeth may be straight, it doesn't mean your bite is OK.  Based off your profile, I would assume you have an overbite/deep bite.  This is often due to the lower jaw being too far back.  I would suggest you see an orthodontist to evaluate your bite.  
If your bite is off because your lower jaw is too far back, a procedure to advance your jaw may be beneficial.  This is called orthognathic surgery. This will help to align the bite, give you more chin projection, and increase the height of your lower face.  You are simulating this when you put the tip of your tongue between your teeth.  It will also help with the deep crease below your lower lip.
If your bite is OK, than you could get a similar result from chin augmentation.  I would not recommend an implant in your case, because it may make the deep crease below your lip (labiomental sulcus) deeper.  A genioplasty advancement may be done to increase the height of your lower chin and bring it forward.
I would recommend against "face lift dentistry" for a variety of reasons.