A safety grab is probably the easiest, just tuck your knees, bring your skis up to you, and grab with one hand underneath and on the outside of your boot. Grab the ski on the same side as the hand you are grabbing with, eg. right hand to right ski.
What type of grab is the easiest or best for different tricks is all personal preference. There are some grabs that my friends are great at that I can't do, and some that I can do that they don't like at all. Just play around and see what is more comfortable/fun for you.
Also, don't get discouraged. When you start trying a new grab for the first time it can take some time to master. Just pick one grab and work on it all day, or however long it takes to get it. Repetition and determination is key to learning new tricks. Additionally, a common tip that applies to all grabs is make sure you bring your skis to you. There are a few grabs were this isn't necessarily true (truck driver and true nose), but generally speaking you want to try to keep your head and torso fairly upright and bend your knees so that you can bring your skis up to where you can grab them. If you're trying grabs for the first time, try to master them while straight airing and then begin to incorporate them into your spins. It makes it a little easier and less complex.