For a long time my wife and I used Saisuke for our Google Calendar needs on our iPhones, but lately we have come to like Calengoo better. Now if you have an iPhone you can use the native calendar feature too, but for us we have multiple calendars and views, so we need an app that can handle those features.
Saisuke was able to do this and we used it for several years, however lately it has become bloated and slow, and we started having problems. We switched over to Calengoo which gave us all the functionality of Saisuke, but without the slowness. Calengoo also has a lot of extra functionality that Saisuke did not, such as changing some of yours views, etc.
There is also the matter of price difference, while Saisuke was $10 for the app, Calengoo is only $7. This is still a hefty price for an app, but when it comes to calendars we find that it is very important to us and worth the cost.
So if you are looking for a good, real app for Google Calendar and are willing to spend some money on it, I would definitely suggest Calengoo. If you don’t need all the functionality and shared calendars, then the native app or even some of the other free apps would probably work just as well.