In occasions such as weddings, there are three main speeches, which are delivered by 3 people; the first one is a speech from the bride's dad which is more often than not emotional and some kind of sentimental.
The second will be the addressing of the bride and the groom to their guests, to their friends and to their family members who are present during the momentous event.
And the last one will be the best man speech.
And since the first 2 speeches where some kind of a traditional speeches and is often times serious, its time for the best man speech to change the people's mood by throwing a lighter message.
In doing this, a best man speech should be a bit funny.
Giving jokes to the people is a good idea too.
But of course, do not forget that you are still in a wedding and this occasion is actually for the groom and the bride.
You should be careful with your jokes or with the words that come from your lips, remember that the affairs formal tone should be maintained but it is good to give or put cheerfulness to the affair.
Best man speech can be of serious and funny, it is actually up to the person who will deliver it, but funny best man speech is better in my very personal view, because you will help the crowd to bring out their jolly feelings towards the event.
But make sure that the content of your speech should be ideal, remember that most of the guests consists of the groom and the brides family members.