Gundam has gone through a lot of seasons. There are some that people liked better as compared to the others. There are some people who have grown old watching this series and they can recommend some that will be appreciated more than others. Zeta Gundam usually takes the top spot. It is also fun to watch because it is composed of 50 episodes.
Some would rather read it and this is perfectly fine too. This has been translated into different languages. Sometimes, this is the only series that people need to watch before they decide to continue on with the rest. This was offered in the year 1985 and people liked it a lot that they still re-watch it now.
There are several gundam seasons and series so when attempting to dive in to all things gundam, it may help to have a guide to get you started on what is and is not worth watching. Gundam Wing, Gundam 00 and Iron Blooded Orphans might be a good place to dive into the franchise since they're in their own timelines and do not overlap so they are much easier to get into than some of the others which require background knowledge.
UC is the newest Gundam and it is recommended that you watched them in production order.