(Pictured is a hive top Styrofoam feeder with a plastic cap/window on the left. Bees access the syrup from under the plastic hood. Syrup is poured into the area on the right. They won't drown with this system).
Initially I had a wooden and metal feeder that sat on top of the brood box. This feeder had holes drilled in its metal bottom that the bees would climb through from below.
These holes entered into a wooden well area where the bees would climb up and over to reach the feed.
A square metal cap would cover this wooden well which would keep the bees from being able to fly freely inside the feeder - making it easy and smoke free to refill without disturbing the hive.
I have two of this type of feeder and unfortunately the seals between the wood and the metal failed on one of them and it created a slow leak which was a problem.
Because of the leak I removed the feeder and instead went with a rim spacer and baggie on top of the top bars as a feeder.
My conclusion from advice, reading and emails from beekeepers is that the rim feeder is really best for cold conditions because the heat of the hive will keep the syrup warm which will ensure the bees eat it. This method has room for only one baggie so if medicating the bees and you want to ensure they take all their medicine this is a good control. But for feeding in general, they were emptying this baggie in 2 days so it was very labour intensive. And then I had to scrape and clean up the extra comb they built too. The biggest drawback too is having to open the hive and smoke to move the bees so you can remove and replace the baggie.
I ended up buying a new hive top feeder, this one made of heavy Styrofoam and I really like it--it's completely leak proof. It has a slit the width of the foam on the bottom and the same type of well where the bees climb up the inside wall of the well and down to access the syrup at the bottom.
It's interesting to note that a temporary solution I made was to remove the metal cover from the wood/metal feeder and put two baggies in, one on each side of the well. This enabled me to leave them double the amount of feed - which they ate in just over 3 days.
(In this photo the bags had just been removed). The bees had free access to climb into the feeder but they did not build any burr or comb in this large space at all. I think it's because it was divided away from the frames in the brood frame that it wasn't so tempting. After 8 days they had not built any comb but I would think that if the feeder was left that way longer that they might have.