I was thinking I'd probably have to get the larger one for the hay. Do they do well with hair pick up?
not sure what you mean by larger...
you shouldn't really need "larger" as in the overall size of the vacuum - if there are literal piles of hay on the floor, it's faster (and easier on the vacuum) to just pick the main bulk of them up by hand and then vacuum up the scraps, so it seems unlikely that you'd ever need to vacuum up more hay than can fit in a 1.5G canister in one go.
if you mean "larger" as in hose diameter, though... if I were you, I'd seriously consider buying from Home Depot even though you can get the discount at Lowe's, simply because the Ridgid vacs have a hose that's 5/8'' wider than anything I could find on the Lowe's site (granted, you could always take a look in-store to see if they have anything better that's not listed online).
if you want something smaller than the 6 gal vac I've got, they also sell a 3 gal one that's $30 and has 3.5 hp instead of 2.5 -
http://www.homedepot.com/RIDGID/h_d1/N-25ecodZ5yc1vZ18g/R-203235053/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=shop+vac&storeId=10051 . the downside to that one is that it doesn't come with extension wands, so you wouldn't be able to use it like a traditional vacuum unless you purchased those separately (they're $8 each and you'd need two to make a full-length hard hose portion -
http://www.homedepot.com/RIDGID/h_d1/N-25ecodZ5yc1vZ18gZ12l0Z12kzZ12l1Z12l2Z12l3Z12kx/R-100638353/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=shop+vac&storeId=10051 )
Ridgid apparently also makes vacuums with a 2.5'' hose, which sounds awesome, but the smallest model I could find one on has a 12 gal canister (which is huge) and is $80 ><
http://www.homedepot.com/RIDGID/h_d1/N-25ecodZ5yc1vZ18gZ12l0Z12kzZ12l1Z12l2Z12l3/R-202554972/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=shop+vac&storeId=10051
all-in-all, I'd say that considering cost, power, size (since you want something small), hose diameter and the desire for extension wands if you want to be able to use it like a normal vacuum, the best option is the $30, 3.5 hp, 3-gal capacity vacuum from Home Depot with the extension wands purchased separately (if you want them). it's powerful/compact, has a nice 1 7/8'' wide hose and is still only about $46 even if you buy two extension wands to go with it. that makes it about the same price as the 6 gallon one I have, but it's half the size (and you don't need a canister > 3 gal for sucking up solids anyway) with an extra horsepower.
if I were buying a shop vac specifically to clean up after bunnies, I would go with the 3 gal one instead of the one I have. (I got the shop vac before I got them - my bathtub drain clogged and there were a few inches of water in the tub... I left it overnight to deal with in the morning and a f-ing roach had the AUDACITY to sneak into my house and commit suicide in the bath water (at the bottom of it, no less!). I'm terrified of roaches and can only clean up corpses with the vacuum, but it died in the ONE FREAKING PLACE that's not vacuum-accessible... so my solution was to buy a shop vac because I will NOT get within a few feet of a roach, dead or alive!)
all-in-all, I've been very pleased with the RIDGID brand vacuum's power and durability.
