Chiller, absolutely. I've brewed nearly 100 batches over 8 years, never used a stirplate. I bought a chiller about 3 batches in, have been using it ever since.
In fact....
I'd buy a grain mill before I'd get a stirplate.
I'd buy a refractometer before I'd get a stirplate.
I'd get a full-size ported kettle before a stirplate.
I'd buy, and then sell, a Cool Brewing bag before I'd get a stirplate.
I'd get a temp controlled fridge before I'd get a stirplate.
I'd build a mash tun before I'd get a stirplate.
I'd build a SECOND mash tun before I'd get a stirplate.
I'd upgrade my mash tun before I'd get a stirplate.
I'd buy an outdoor propane burner before I'd get a stirplate.
I'd build a 6-tap keezer before I'd get a stirplate.
In fact, I've done all those things, and I've brewed award-winning beer.
Really, you don't NEED a stirplate for anything. You can just use a bigger starter and manually agitate it. All the stirplate does is help you grow up more yeast with less wort.
And if you REALLY want a stirplate but you're short on cash, you can build one for approximately $0 if you scavenge the parts. See here for an example:
http://www.wortomatic.com/articles/Building-a-Basic-Stirplate-for-Yeast-Suspension
I've actually already scavenged just about all the parts I need, but laziness has won out. I actually make starters pretty rarely, and instead brew half batches of low-gravity beers and then use the yeast slurry.
I also agree with the posters above, US-05 is a fantastic yeast. I use it a lot. I'm also a cheap bastard and reuse my US-05 slurry a lot.