Why we like the looms:
Knit is a LOT stretchier than crochet - making it easier to get the hats on delicate little heads.
The pegs on these sock looms are close enough together AND they're adjustable so you can make hats to fit nearly any size! (30 pegs for a 20 week size hat)
These flower looms are the exact right sizes for our crochet outfits
These are a lot easier for some people to use, especially kids.
Things we don't like about the looms:
The flower looms are a little bit finicky. I LOVE the small and medium size, but the big size is mostly a pain. My hands are too small to really hold it in one hand - but it's not really big enough to rest on anything while I'm holding it. These don't have grooves for the hook so you just have to finagle it till you get it to work for you. I only loop around 4-6 pegs at a time and use one thumb to hold it on while I work on the rest. There aren't flat pieces on the pegs to keep the yarn on. But the tiny one is the right size for a 15-16 week size outfit - something we haven't been easily finding.
Personally I'm not a huge fan of the adjustable sock looms. But I know some others really like them.
These knit hats take me a lot longer than crocheting a hat. More than double the time for the big one.
All in all - we're finding the looms to be a great way to get some tiny hats that are really stretchy. There are pros and cons to each kind - but they are working really well!
Large (20 week size) hat: about 4 inches of knitting
Medium size hat: about 3 inches of knitting
Small size hat: about 2 inches of knitting.
Small size fits on my thumb
Caron Simply Soft yarn works well on these types of looms. It isn't the best though - smaller baby Sport Weight yarns work better - but to match an outfit - you can definitely use the Simply Soft yarn. Also there are sock yarns that are a lot thinner and I've heard those work really well too.
You can make a brimmed hat - but you will lose lots of the stretch. On a large brimmed knit hat I found it stretched almost the exact same amount as the crochet large hat. So that is definitely an option.
For the medium and small hats I recommend not doing a brim and just letting the edge roll up (it will kind of happen anyway) because the smaller ones need the stretch so much more.
These two hats are made from the same yarn. The brimmed one stretches 1/2" less than the one with a rolled up edge. Not a big problem for the bigger hats - but the extra stretch is so helpful on the tiny ones.
I compared a knit hat with a brim and a crochet hat (both large sized) and found that they stretched nearly the same. So for me it's a lot easier to crochet the bigger hats and knit with the loom for the smaller hats.
Christine at Sew Much to Share, Davis County has a lot more info about different looms and yarn types. She's also got lots of knitting experience (this post is everything I know about knitting) and she has lots of other patterns and angel baby info on her blog.