wipekitty

The big differences - from what I can tell:

• Avail 1 has a 'composite' (carbon fiber) fork; Avail 3 has aluminum. Carbon is said to provide better shock absorption than aluminum, thus improving comfort. (Most aluminum bikes come with a carbon fiber fork.)
• Avail 1 has a slightly upgraded groupset over Avail 3. Avail 3 has Claris, which is kind of entry-level Shimano. Avail 1 has Sora, which is the next step up. I personally have not used either, but there's a chance that Sora will provide easier and more reliable shifting.
• More on Claris vs. Sora: Claris has an 8 speed cassette on the rear wheel, and Sora has a 9 speed cassette. The range is the same (easy to hard gears), but 9 speeds allows for additional intermediate gears, which can be helpful on flat and rolling terrain.
• Avail 1 has a different (better?) wheelset. Between the wheelset, fork, and groupset, it is probably a bit lighter.

Assuming you want to buy new and from a shop, it would not hurt to check out and test ride some of the other brands that might be available at nearby shops. Trek and Specialized are also ubiquitous; Specialized no longer does women's frames, but makes all frames available in tiny and large sizes. I think for the under $1K range, the Avail 1 is a good deal.

Used is also an option for getting something really nice for under $1,000, but the tradeoff is that you'll need to know something about bikes to evaluate the purchase, and unlike shop purchases, used does not come with annual tuneups and warranty support. It can still be worth looking into, particularly since smaller-sized bikes are harder to resell and can often be found for cheaper than the standard 52-58cm sizes. Bike and tri clubs can be good places to poke around for used bikes that have been maintained.