Sippy Cups: should I buy more plastic ones?

I have always been in the camp of plastic = bad when it comes to contact with food and water. So why is it that when I reach for a sippy cup for my son's milk I am reaching for a plastic one, even though we own 3 stainless steel sippy cups??  My current working theory is that they are a pain in the #$% to clean, but upon further inspection, they really are not! There is one extra small step in the cleaning process (I wash all sippy cups by hand because the dishwasher never really gets them as clean as I like...I live in an old rental house with old appliances!) Anyways, I'm at the point where the 3 plastic sippy cups I own have been chewed through to the point where the spout of one leaks 100% of the time. This negates the whole purpose of a sippy cup when your toddler holds it upside down...;on purpose!

Why is my child sick again???

I thought I had done everything right, and maybe I had? I breastfed for 18 months, exclusively for the first 6 months, I feed my child very healthy foods (broccoli, fish, sweet potato, chicken soup, etc) and very few unhealthy foods (he is 19 months and has never had cake, cookies, ice cream, or any other sweet) and I even give him basic supplements (cod liver oil, vitamin D and probiotics). I even avoided Purell and other hand sanitizers because they supposedly either don't kill all the germs or create "super bugs" (I am still unclear). I make sure he is well rested, well hydrated and that he gets plenty of fresh air and exercise in addition to multiple hefty doses of "mommy love" each day. So why is my child sick again?