Great question.
The answer is "it depends".
I'm on Southern Vancouver Island and about 10 years ago, I was asking exactly the same question, so I've done a lot of research into the area.
An important thing to remember is that there are breeds and there are individual flocks. I noticed in our area, many of the reproductive traits (like twinning or easy birth) common to the breeds weren't as strong as I expected. A difficult birth requires human intervention to save the life of the lamb and the ewe. Traditionally, Ewes (and rams - as the sire can have a strong influence on head size of the lamb) with a history of difficult birthing would be culled to ensure that these traits don't stick around. But nowadays, with smaller flocks, we get emotionally attached to each sheep and we think "she's so sweet, let's just keep her and her lamb and see what happens next year" (I admit, I am guilty of this)
Questions:
- have you had sheep before?
- do/have you other livestock?
- what will you do will the fibre?
- will you take it to the
local mill in Sidney?
- will you hand process it?
- will you
sell it to fibre artists?
- what kind of fibre artist?
- will you be selling breeding stock?
- if so, what will you feel like when you discover your lovely lamb you sold soandso is living in a wallow up to its chest in mud and being wormed once a week with toxic dog meds?
- do you understand the difference between salt and minerals for sheep care? (I really wish this wasn't a question I had to ask, but it is a huge thing people get confused about)
Most importantly, what will you do for medicine/care for those times when you need an expert? Vets that are willing to treat sheep are hard to find. Recent laws in BC mean we aren't allowed to buy worming meds or antibiotics without a vet. Good prevention means you probably won't need it, but it's also illegal to deny an animal these medicines when they need it which can lead to criminal charges. It's very complicated and political here.
Shetland and Icelandic are both old breeds and both have a high tolerance for variation in their diet. They have different mineral needs. Have a look at Pat Colby's (sp?) writing on natural sheep care where she talks a lot about the different mineral needs by breed and how having the right minerals can prevent many health issues.
If you are keeping them with goats, check the copper tolerance for the breed. Copper overdose will kill a sheep quickly, but different breeds have different tolerances. Something like a Black Welsh Mountain can tolerate the same amount of copper as a goat - SO LONG AS THE COPPER is separate from other minerals and salt and free choice.
Fleece-wise, the difference is huge. Before choosing a breed, I recommend getting one of each and working with it by hand. Skirting, sorting, washing, carding (with hand carders) and combing (with wool combs), spinning (both drop spindle and wheel), then make a wearable bit of clothing. Wear it every day for a month, except for washing, and see how it holds up. They are very different to work with and create very different cloth.
Both fleece types have different characteristics when mill processed. They have a dual coat and the short fibres act differently to the long ones which can make some beautifully textured yarn - or pill terribly - depending on how it is processed. The local mill is very good and Tracy or the staff there can walk you through the options.
Price may also be a huge factor. Think about registration - is it important to you? It makes no difference as to the quality of the animal and quite often animals are killed because they are the wrong colour or shape for the breed standard. Some of my best animals are culls that were the wrong colour to be registered.
Sheering, both breeds can be shorn twice a year, but this depends on your goal for the fibre. Too short a fibre.
Motherhood - depends on the farmer you are buying from more than the breed these days. Does the farmer cull for difficult births or bummers (orphans/rejected lambs)?
Richer hay demands? Not sure your meaning here. Hay demands in the PNW are higher in the summer (when hay is more expencive) and when snowing. The hay demands will depend on your location and forage. You don't want a nitrogen-rich hay for sheep.
Wetter - again, depends on the farmer you buy from. Do they cull for feet issues? Correct mineral balance for your area can have a huge influence on this.
Lifespan - not sure
Microns - What I say about this is contrary to popular opinion. Most of my animals get finer fibre as they age but most farmers around here claim it gets thicker. Animals we got as adults have much finer fibre after a few years here. The shearers remark on this as they keep samples from different farms over the years. I firmly believe that diet and care influence fibre thickness far more than age.
For myself, I went with Icelandic. They are very nice with a wonderful temperment. Good healthwise but sensitive to SE defficency (as all sheep are here since we don't get SE in our soil). I think fibrewise, I would have been happier with Shetland, but very quickly, I moved away from the duel coat breeds and went with Black Welsh Mountain as they are also very good in our conditions, have less demand for SE but also have a high copper tollerance range as I had planed to run them with my goats. After a while, I discovered that the BWM had too high a copper demand and their fleace suffered from lack of copper. Also the Icelandic and BWM weren't good at flocking - they scatter.
I've now moved to Cotswold. The fibre sells for more and the personality of the breed is far more affectionate which turns out is the biggest quality we want in a sheep - afection and self reliance in perfect ballance.