Hi, Cass, welcome aboard!
Brace yourself, I suspect you will get LOTS of responses to you questions! I just wish the answers were as simple as it seems they should be. In your stated price range of $100 to $150, there are some very good guns available. Problem is, I can't think of a one that's really good right out of the box. Most spring guns need a lengthy break in period, 1000 or more shots before they settle down and smooth out. Most in your price range also have pretty poor triggers, which means extra cost to deal with. If you're used to target .22's, you WON'T be happy with the stock triggers on most (any?) lower priced air rifles.
If you go springer, there's a learning curve, and a lot of shooting needed. Spring guns don't shoot like anything else, and being used to powder burners is probably a disadvantage. Also, air guns can be very picky about which pellets they shoot well, so you need to be willing to invest in the time and cost to find which works best in the gun you choose. And watch out for scopes, the same thing that makes them challenging to shoot makes the extremely tough on scopes. Springers recoil back like a normal firearm, but they also recoil forward. That's what tears up scopes.
If you haven't looked aroud the forum much yet, be sure to check out the Product Reviews and the Library. Lots of good info there, you'll probably find answers to questions you didn't even know you had.
To actually answer your question, my personal experience is with Gamo's, RWS, and Beeman, in order of increasing cost. I think the Gamo guns are an excellent value, but they need a better trigger. The stock trigger is lousy, heavy and inconsistent. Expect to spend $10 to $30 to fix it. They respond very well to tuning, but other than the trigger, they're not bad out of the box.
RWS guns are a definite step up in quality, but personally, I don't know that they're as good a bang for the buck as the Gamo guns. The stock trigger is better, but I was never able to get mine how I wanted it. And they tend to ship with minimum lubes, so they can be pretty rough to shoot at first. A lube tune was a big help with my 350, but I still ended up selling it. Just too much gun for my needs.
Despite what Pyramyd said, I've heard good and bad about the Crosman rifles. Luck of the draw. One thing to watch for, lots of guns come from the same source, mostly China, but carry different names. Again, check out the Product Reviews. Vince and some of the othees have have done an excellent job sorting some of this out.
If I was in you position, I'd get one of the Gamo Hunter 440's for $120 from Natchez.com (if still available), a Leapers or Tasco scope, and either a trigger insert from Rich in Mich. or a new blade from Bob Werner, aka CharlieDaTuna. Read all you can, and shoot it a LOT! And if you have any question, post them here. This is a great forum, and seems to be unique the way it feels. Check around some other forums, you'll see what I mean. Good luck, and have fun! Keep us posted on what you end up with.
Dave
OOPs, almost forgot. I'd go .177 for a first air rifle. For what you want to do, it'll be quite sufficient. Check out the Hunting gate for more info.