You'll probably get a variety of answers.
My opinion, the 'best' protein supply is natural (lean beef, chicken, tuna, etc). But, if you're not able to mix a shake, you probably won't be able to grill meat either LOL.
I'm not familiar with the tablets, I've used either powder or protein bars. The protein bars are convenient to take along if you can't make a shake, but can be expensive. However, there are recipes online where you can make them home-made using whatever protein powder you're currently using...some of them are pretty good, and a lot cheaper than if you were buying them from GNC or where ever. Google 'protein bar recipes', or I'll see if I can't find that site I found them on a while back, there was one site that had several different ones.
ETA:
some google results