UPS is faster and cheaper for almost all package greater than 2 kg. The only significant downside is that UPS charges on the basis of the greater of the actual weight or volumetric weight. The rule to calculate the volumetric weight is 139 cubic inches = 1 pound. For example, if your item weights 20 lbs, but has dimensions of 24" x 24" x 24" (13,824 cubic inches) then the shipping weight will be 100 lbs (13,824 / 139). I have a button on the right hand side of my order page (Shipping Cost Calculator) that will help you calculate the volumetric weight based on the box dimensions.
UPS charges additional fees (surcharge) for the following:
My shipping cost calculator takes these surcharges into account when estimating the shipping costs.
The one minor limitation with UPS shipping is that it UPS packages can't delivered to a PO Box or Parcel Locker. You will need to supply a physical street address.