Hi ; wanted to check when we create a bundled SKU which is a better method - kit or item group especially if it’s non inventory for sale .

Groups are much less complex. They don't hold pricing, either, so the sum of all the parts will give you the price. Groups are not web publishable, so best for internal use only. Kits offer more complexity. The pricing structure lives and exists on the kit itself, which means you'll need to maintain the pricing over time (as components fluctuate up or down). You can publish them to a Web Store (if you have one, or aspire to have one).

You need to understand the difference(s) between group and kit to make the decision. @Dan Curtis has pointed them out.