I always use usps for all of my shipping needs. They are twice as cheap as ups. Plus you can get free boxes and labels shipped right to your door. they will also pick up your packages for free so you don't have to go to town to ship them...
If you are selling heavy items you might want to consider usps flat rate priorty boxes and rates..You can ship anything that will fit into the box up to about 70 pounds for around 8 dollars...For smaller items try using the rated priorty shipping rates as they are much cheaper than ups...This is a good way to get some of your ebay listing fees paid for..By this I mean that alot of sellers list about $1.50-2.00 dollars for shipping and handling fees..This shipping and handling fee normally covers the cost of the packageing/boxes that the seller has to use to ship the item..If you are using usps priorty mail, then you get the boxes for free. So you can then use that $1.50-$2.00 shipping and handling fee to help pay your listing fees....Just a tip....
If you are going to continue to use ups, then I completely agree with GRboutique, enter the acutal weight and size of the package and use the shipping calculator....Having lower and/or competive shipping rates will increase your sales...Buyers pay close attention to what they are being charged for shipping, and if they see you are higher than your competitor they will buy from them....