Truthfully, It doesn't really matter what missile / rocket Ukraine gets, as long as it meets these 4 characteristics.
1. It has range between 200-300km, giving Ukraine the ability to execute strategic strikes in all of Ukraine, Crimea and when necessary, western Russia.
2. They are available in a quantity that will allow Ukraine the potential to saturate Russian air defense systems in selective regions. Russia has quality air defense systems. Ukraine needs a workable number of missiles to account for the fact that, inevitably, a good number of them will be shot down on the way to their target.
3. They have to be highly accurate, with a low probably of missing their intended target. Not only are many of the key Russian assets in the middle of populated areas, Ukraine all doesn't want the bad publicity associated with killing civilians like the Russians have. Furthermore, they can't afford to miss their strategic targets when they do get through Russian air defenses.
4. They have to either come with a launch platform, or be compatible with one of Ukraine's existing platforms. This one is, obviously, self-explainable.