Botox Vs Fillers for Minor Forehead Wrinkles?

Fillers would be better for you because the wrinkles are visible even when your face is in a neutral expression. This means that they are "static" wrinkles, and fillers is the right treatment to smooth them away. If the wrinkles appeared only when you made a facial expression, like frowning, then Botox would be more suitable. Botox treats "dynamic" wrinkles.

Generally, Botox is the treatment of choice for the forehead area, as it can be very difficult to place fillers correctly there. I would recommend starting with Botox to see if your wrinkles soften or even disappear, and if after a few Botox sessions you are still unhappy with the appearance of your wrinkles, you could try to find a highly skilled dermatologist who could potentially place a small amount of filler. Often, Botox works very well to soften lines that aren’t too deep yet.

Thank you for your question. Botox can be used to soften the appearance of lines and wrinkles that deepen with expression. These include the horizontal lines of the forehead, the frown lines between brows and the smile lines (crows feet) on the sides of the eyes. They typically last 3-4 months. Fillers on the other hand is very effective at filling in the lines or shadows when you are not expressing yourself. They can also be used to shape and lift the face. I would recommend that you visit with at board certified plastic surgeon or dermatologist in your area to discuss your treatment options so they can be tailored to your concerns and goals.

Botox works to relax muscle movement and prevent lines from becoming a "fixed feature" in the face.  It can not take away the lines that are present with a flat affect.  At 30 years old, I doubt your lines are very deep.  I've found that my patients with fine lines experience a softening in the appearance of the lines after 1 treatment.  After 2-3 treatments of Botox I've seen lines completely go away.  I'd advise getting Botox 2-3 times before considering filler.  For safety reasons, it's best to avoid using filler when possible in the forehead particularly.

  In general, I  prefer Botox in the upper half of the face and fillers in the lower half because they are more effective in these areas.

Botox will help keep the lines from deepening and will help a filler last longer in any area that a line forms as a result of skin crimping with muscle contraction.  If the lines are shallow and directly reinforced with muscle contraction, start with the botox injections and you may not even need a filler as your skin will grow in new collagen itself

I may offer an Injectable Filler treatment to someone with deep forehead wrinkles that do not fully resolve with BOTOX. If you can only see them in certain lighting, and if they're small, you'll likely be very satisfied by a BOTOX treatment.
I hope this is helpful for you. 

Dysport or Botox is very easy and works well for forehead lines. Cost is roughly $300 and lasts about 3-4 months. Fillers can be done later if the lines are still visible. 

fillers don't work very well on the forehead lines compared with Botox. Sometimes the fillers bead up visiblly or move to the sides of the wrinkle and make it look more apparent. Wrinkles that are present at rest can improve with Botox if the treatment is maintained every four months or so, such that the effect is worn off and the muscle activity doesn't return. The creases of the skin improve because the muscle underneath doesn't make it "accordion" . This is similar to those people who have had either a stroke or Bell's palsy and don't move a part of their face as much, they can see improvement in those lines. So whether the lines are present at rest or only with muscle activity, Botox can help. Not all people are candidates for Botox of the upper forehead as it may lower their eyebrows and eyelids. Or there may be a crease above and close to the eyebrow where Botox shouldn't be injected. In these cases fillers may be used, often with good results.

Botox or Dysport is definitely the first line of choice for forehead wrinkles or any wrinkles from the eyes and upwards.
Only after the paralytics have been maximized would I consider use of fillers for this area.
Good luck.