What Ullsock said plus
Over the last 10 years I'v fished both rivers five to six weeks. Both rivers are superb steelhead rivers. However they have a different character. The DEAN flows between steep Coastel mountains and has this blue greenish open 'freestone' look. You can almost feel and smell the salty blue of the Pacific nearby. The fish are brighter (generally spoken), the air is fresher. And you will fish in more summer type conditions since you'll fish earlier in the BC season and more in a coastel weather type.
The Babine is much more a darker forrest river with ist dark bottom of ledgerock, 'mossy' rock struction. Fish can be very fresh, but genarally spoken they will be a bit deeper in color (still magnificent fish, no complaints....) The temps can be cooler and in second half of october there can be snow on the ground.
After you've made a couple of Babine trips I can only suggest you'll give the Dean your best shot.
I agree with Ullsock's post and will add the following: The fishing on the Dean has not been good the last few years. Some of it has been river conditions but last year had good water and no fish. Doesn't have any thing to do with this year but the trend is not great. Babine fish are bigger. Water temperatures on the Dean are better and dry fly/skating can usually be done with some success. If you haven't been to the Dean, you need to go.
A couple of specific points about Hodson's: Bring your own booze, if you drink, and a lot of it. Give your leftovers to the guides. The ladies that clean the cabins pour any leftovers down the sink

Also extra books in case the river is out. If you have a choice, stay in the lower camp and don't go to the upper camp. Every year is different but in most years there are not many fish in the upper camp until August. An exception to this is if the lower river is out. The upper can then be the only fishing on the river.
The Airport Fairmont is the best place to stay the night before your trip. They will shuttle you over to Millionaire the next morning and lay out a great breakfast spread. If you dine there, tell them you want in and out in an hour, unless you don't, or your dinner will last 2+ hours.
Have fun.