I got my first bees in Decemeber of 2012 (yeah, kinda of a strange time, but...
). I used ziplocks a couple of times as suggested by my mentor. He uses them successfully and I'm sure thousands of other beekeepers do, too. But, I had some problems and quickly moved to quart-sized mason jars...I've never looked back.
With jars you're probably going to need a "shim" to enclose the quart jars so that it is protected from the elements and out of reach of robbers. I use inner covers with telescoping covers and the "shim" goes on top of the inner cover and below the top cover. I use a medium box/super as my shim when feeding with quart jars. I screen over the escape hole and the extra 2-3/4"/70mm hole that I drill in the inner cover (sometimes I feed two quarts at a time)...I use #8 (1/8") hardware cloth for the screen. The screening keeps bees from clinging to the jar lids and also flying up out of the holes when I remove the jars. I block any notches in the inner cover that allows bees and other critters to come inside the shimmed space. Feeding through the feeder holes in the inner cover is a good way of putting feed right above the cluster.
I bought a few one-piece "store bought" feeder lids to see how they worked...they work great and were just a little more expensive than regular one-piece lids. These lids have 13 small holes punched into them. I think that half that many would work just as well. I've read where different numbers of holes affect the feeding rate (makes sense to me) and that the different feed rates stimulate the bees in different ways...that's something else that this newbee (me) has yet to fully get a grip on. I'm thinking it's something like fast 1:1 feeding promotes brood and wax creation whereas a slower rate of a thicker syrup tends to put them in a more conservative mood. I've still got a lot of learning to do!
If you go with ziplocks you will need a short shim but rather than feeding on top of the inner cover I've seen most people that feed that way put the ziplock directly on the tops of the frames.
I haven't had any jars to leak on me that I'm aware of but I've always had them under the top cover so no sun exposure. Tighten the lids firmly. The only problem that I had was actually feeding too much and too fast and finding during last years apparently enhanced swarm season that I chased several swarms.
The biggest negative aspect of jars is that they're glass and will break...I haven't broke one, yet (now watch me go break some!). Something else that will happen if an empty is left on the hive too long is that the bees will seal the holes in the lid with propolis...just stick the lids in the freezer for a few hours and then use a straight pin to punch the hardened/frozen chips of propolis out of the holes.
One-piece jar lids are very nice in that they sit more flush to the screen. You don't want a gap between lid surface and the screen or the bees tongues might not be able to get to the syrup. An old beek shared a trick with me regarding using two-piece lids...he said to turn the lid upside down in the ring...so that the gasket faces out and against the ring and the center area of the lid protrudes outward rather than inward. This moves the surface of the lid closer to the screen (and bees). I haven't tried this but he says that he's had no problem with it...he does this on his own hives and last time I saw his yard he probably had 30 hives there. YMMV.
I'm not sure how many hives you're feeding, but I needed just a quart of syrup the other day for a small cutout. I'm pretty sure that it was 3 cups of sugar to 3 cups of water that made almost a perfect quart volume. I'm going to have to try it again to be sure, but I think that's what it was. Also, dissolving some crushed up Vitamin-C (ascorbic acid) in the hot water will bring the pH closer to that of honey and will also help retard fungus from growing in the syrup for a while...it's good if you make more than you can use quickly.
When you're feeding keep a monitor of how much the bees have stored....you don't want them filling the hive up with sugar water!!!
I like jars...but everybody has there own preferences.
Jars are durable (within reason), re-useable, have good visibility for monitoring, and you can use them as a glass for sweet tea when not feeding bees with them.
I'm just a rank newbee so take all of that with a grain of salt, it's subject to correction by somebody that's smarter than me!
Best wishes,
Ed