Hello, I think I can help.
We have 6 duckies and I would compare them as follows.
Very Stable, very durable, a bit boring for an agressive surfer type. Heavier paddlers sit in water all day. Quality valves. A well built, long lasting boat.
NRS: A bit cheaper material and a different design. Will not hold heavier paddlers well. Decent valves.
My favorite boat. Holds large paddlers well. A bit pricey at $1100 or so. Very well made, quality materials, durable anchor points. Sleek design allows it to surf well and it tracks like a dream. It is slightly less stable than a hyside or NRS.
A real deal at $500 or less. A slightly deeper hull design than the lynx but still a great surfer. Decent materials except for the tie down anchors. I ripped one out the first day when I flipped and the rear thigh strap attachment point ripped out. Cheap valves. Bladder in a condom type design like all aire boats. This is a good boat for what you want I think, although I would highly reccommend putting in some D-Rings for the thigh straps.
There are duckies made by many other companies as well. Wing, Sotar, Shredder and others. I would also take into consideration the pvc-vs-hypalon thingy too. The hypalon boats like hyside and nrs generally store rolled up better for long periods of time and they are also easier to patch. The PVC boats are stiffer and surf better, but shouldnt be stored rolled up for long periods of time as cracks can form in the pvc.
Reading what you want for a loaner boat for when friends come over I would recommend the Aire Tomcat. Its a very good deal for the money, and is still a riverworthy craft. Although if you choose thigh straps I would install 4 small D-rings to attach them to. You can also install adjustable foot braces as opposed to thigh straps. You need to order these items seperately as they do not come with the boat.
I run the Taos Box, The Numbers, The Gorge, and even an occasional class V creek in my Aire Lynx. I use thigh straps only. I also do Westwater, the Pilar Racecourse and other easier runs. It reaches a point at higher flows when the bigger waves and holes need to be avoided to prevent a swim. (duh!) I havent done the Numbers or the Gorge over about 2000cfs. I did the Taos Box at almost 6000 this year.
Make sure you instruct your duckiers about self rescue (flip boat back over and climb back in), and make sure they wear proper clothing. I typically will swim 5 or more times, usually when surfing. A rookie might swim a lot so make sure they have some gear! Wetsuit, booties, paddle top, helmet etc....
As far as a "better" duckie it all depends on your weight, paddling style, and the types of rapids you want to run. There is the newer Aire Force duckie that is basically a decked duckie that you can roll. I like my lynx because I can surf and do class 4. I can also put a drybag in the back and go for a multiday self supported trip, which me and several of my friends often do down the gunny gorge. I like the tomcat because its just almost as good as my lynx, for half the money. Just remember the cheap tie down anchors it has and dont trust them too much.
Hope this helps!