(1) Desired.
(2) Preferred.
(3) Agnihotra, Tap, Truth, Yagya, Daan, hospitality, meditation etc religious activities are called Isht.

Isht Devtaa
A favorite Devtaa of a person.  Isht Devtaa is the Devtaa or the Deity to whom you like most, you love most or yo remember most in the situation of your need, problems or otherwise. This Devtaa may be different from your family Devtaa (Kul Devtaa).

Regarding the Choice of Isht Devtaa
Choosing your Isht Devtaa yourself if like a patient choosing his medicine himself, how much of sense does that make to you? Its a fairly deep and vast concept to explain in short, but here are a few hints. It is a strange thing, almost call it a game of Maayaa... but usually a person is unknown to him till he meets a master, and on the contrary it has been often found that Isht Devtaa is the Deity people don't like by default. Still, out of 33 Crore Devee Devtaa, there is always one Devtaa who is like key to your mind and soul.

It is like if your brain has 33 Crore Neurons, then there is only one Neuron that will vibrate in the same frequency as that of your Isht, and in turn light up all the remaining Neuron, make you enlightened. On a Subtle level, the master has to evaluate your Aura, your Prakriti and find out which deity, which vibration is the key to your mind, hence destiny.

That Devtaa may be so called Great Devta as in Tri-Dev (Brahmaa, or Vishnu, or Shiv) or even someone at the level of Kul Devtaa, but it will be only his frequency that will open up your mind and illuminate your soul fastest. Like if Krishn is your Isht Devtaa then you may worship Taaraa for 10 years, still chances of success are less and limited, but if you opt for Krishn straight away, then within an year you will achieve what you cannot through others in 20 years. That is true both for material and spiritual growth.

That is why it is best to meet a master, tell your problem and let him decide what solution to opt for it. Like these days it has become fashion to opt for Bagalaamukhee for every court case... but the truth is, only master knows which Vidyaa will give "you" the fastest relief. Someone may be told Kali, someone else may be told Ganesh... and so on. So let the master decide for you as who is your Isht Devtaa.