Last night I went to my local magic club and during the part where people perform tricks I noticed that some people sat and other people stood. This is a small thing, but an important thing when it comes to actually doing the trick.
If you are sitting when you do the trick, but practice standing, you’ll have a hard time as the range of movements in your arms is limited by the table top. If you practice sitting and perform standing, you upper body will now slouch.
Going from sitting to standing I think it an easier transition to do. However I recommend practicing to perform standing. Here’s why, you are more visible standing, and it’s more versatile. When you aren’t bound by a spot to sit, you can choose where you are going to do your magic trick.
I guess the main advantage sitting gives you is lapping, where if you are going to do that then YES sit. However if you do a more formal show, you should consider a more formal approach and do it standing. A great example of this is Shin Lim’s act:
Everything that would have been done sitting 20 years he’s doing standing and it really plays a lot better.
TLDR: Perform standing, unless you have a very good reason why to do it sitting.