A leaf bud (we'll say vegetative bud) is composed of a short stem with embryonic leaves, with bud primordia in the axils and at the apex. Such buds develop into leafy shoots. Leaf buds are often less plump and more pointed than flower buds.

A flower bud is composed of a short stem with embryonic flower parts. In some cases the flower buds of plants which produce fruit crops of economic importance are called fruit buds. This terminology is objectionable because flowers have the potential for developing into fruit. This development may never occur because of adverse weather conditions, lack of pollination or other unfavorable circumstances. The structure is a flower bud and should be so designated since it may never set fruit .. Understanding which buds will bear fruit and which will form leaves is a good first step.There are essentially two different types of bud on a fruit tree:

• Growth bud:  a bud from which leaves or a shoot develop
• Fruit bud:  a bud that flowers and then yields fruit

It is a difficult ask, probably more triggered by the rate of influx of auxins over gibberellins , and this is the reason , many times, reproductive buds appear so instantly without any visual appearance of vegetative buds or usuallly , vegetative buds come first followed by reproductive buds in most of the cases...Interesting question..

Externamente, algunas yemas vegetativas presentan una forma cónica alargada, mientras las reproductivas son más abultadas y cortas sen forma de barril, su posición en la axila de la hoja y en el tallo también varía según la especie. Con una disección bajo el microscopio es posible distinguir entre primordios foliares (yema vegetativa) y los primordios de los estambres (yemas reproductivas) principalmente. Los primeros son puntiagudos o acuminados y los segundos suelen terminar en formaciones globosas correspondientes a las anteras.

http://www.waldeneffect.org/blog/Flower_buds_vs._leaf_buds/

In general, flower buds are fat and round while leaf buds are more pointy and less significant. The differences really become obvious at the time when the flower buds are swelling up in preparation for opening, in contrast to leaf buds that are still dormant.

Flower refers to a part of the plant that contains the reproductive organs. It is often surrounded by colorful petals and sepals. Bud refers to an elementary stage of a leaf and flower. It occurs as a small auxiliary or terminal protuberance (stem) on a plant.

Thank you @ Anoop Kumar Srivastava @ Hayati Akman @ Eduardo García-Villanueva @ Meera Kumari ... I am working with Roses, so what I learnt in my lab, want to share with the public. Hope I am right.

Though the difference between leaf and flower bud depends upon species, here are some common points that can help someone pick the desired bud. (most of them are described by the answers above): [Size, color, position]

1) flower bud is more fatter or bulkier or plumper than the vegetative buds.

2) The color of both is also different; for instance, in Roses, the flower buds have some white powdery (hairy) appearance on its top, while the leaf buds will have the normal appearance {this is the major differentiation point}.

3) Position of the bud is also important, but that depends upon species. In Roses, the flower buds will always appear in the apex, and never anywhere in that branch, whereas the leaf bud can appear anywhere. This point will help you when collecting the samples, so you will only search apex of the branches. (In roses, a branch terminates after giving out a flower bud).

I also have some experience with Peach trees, in which flower bud is very easy to find (because the flower bud opens before the leaf buds). The buds appear in the pattern flower-leaf-flower. Same is the case in other stone fruits and some temperate deciduous trees.

If I am wrong, please correct me. Your suggestions are highly appreciated

Here I translate the answer of @ Eduardo García-Villanueva so that other can read it too:

Externally, some vegetative buds have an elongated conical shape, while the reproductive buds are more bulky and short barrel-shaped, their position in the axilla of the leaf and the stem also varies according to the species. With a dissection under the microscope it is possible to distinguish between leaf primordia (vegetative bud) and the primordia of the stamens (reproductive buds) mainly. The former are pointed or acuminate and the latter usually end up in globose formations corresponding to the anthers.

Here is my work in the image files, I thought to share with the public. Now I can differentiate between the buds easily. Thank you guys

n general, flower buds are fat and round while leaf buds are more pointy and less significant. The differences really become obvious at the time when the flower budsare swelling up in preparation for opening, in contrast to leaf buds that are still dormant.

Flower refers to a part of the plant that contains the reproductive organs. It is often surrounded by colorful petals and sepals. Bud refers to an elementary stage of a leaf and flower. It occurs as a small auxiliary or terminal protuberance (stem) on a plant