I have tried boots, lansinoh, medela and the japanese brand sold in BNM/birth.hk
The japanese one-- the plastic is thick enough, and it has a pointed end, milk can be drained out easily after seize the end. However, it has no zip. I always worry that milk will leak before it freeze but it have never happened yet. It is about $3.5@
Medela--the safest one. Thick plastic, tight zip, able to stand up, never tear or leak. However, it is very expensive, almost $ 5@. Moreover, it is quite small in size, ~ 5.5 oz only
Boots--the cheapest one, ~ $1-1.5 @. However, it is also the weakest one. This is only one I found leakage happened. Milk leaked from the edge.
Lansinoh-- also sold in baby outlet and product of thailand, ~ $2.5-3@. The plastic seems as thin as boots but it is little bit stronger. No incident of leakage yet.
I think if you need to travel for a long journey, better use a stranger one.
On last point, you can directly pump the milk directly into the milk bag (boots/linsinoh/medela), if you use medela milk pump.
I think you can do it all types of milk bed that with wide opening. In stead of fitting the collecting bottle with the pump, I just let it drain into the bed opening directly and hold the pump and the bed together. For medella milk bag, it has a sticky tape, so it can stick to the pump. It takes u sometimes to handle the technique. Although it is not tight as if with the bottle, the milk is still clean and not contaminated.