Best bag for commuting

I'm starting a new job in January, as its 15 miles each way I'm gonna ride in, any ideas on the best bag for carrying my gear.

Panniers? Lowers centre of mass, no sweaty back, nicer to carry bigger loads, etc.

Edit: what are you planning to carry?

If you're going the backpack route the Deuter Race bags are good

Sorry I was a bit vague, lunch, phone, a book, not much as I'm provided with a uniform (will need to carry it back to wash it) other stuff like shower gel and deodorant (when it runs out) I've got a locker at work. Thanks

Pannier, saddle or rando bag is my advice. Rear rack & an ortlieb back roller is a popular choice. Or front rack and an ostrich bag, they're on sale at planet X atm. Or a large carradice saddle bag, they have two different qr options so you don't have to fiddle with straps etc

^ I’d still recommend this. But if you want a rucksack, I like my Alpkit Gourdon. Waterproof, light and cheap as chips. But you will (almost) definitely get a sweaty back with a rucksack.

I run hot, so prefer to carry all my load on the bike rather than sweating with a rucksack; for 15 miles doubly so. If you have rack eyes then a single pannier should take all that with no problems; if not, then this kind of load is exactly what Carradice saddlebags were designed for and have been carrying for 80-odd years. If you might need to bring a uniform back I'd go for one of the larger ones: maybe a Pendle or Nelson.

I carry a similar load and went from a Carradice Barley to an Ortlieb pannier on a rear rack. Can't really go wrong.

One more for the Alpkit Gourdon, was a cheap at £22 5 years ago, now up in price a bit to £32 but still great value. Takes lunch change of clothes and a bit of shopping at a push.

I'd recommend the Thule pack'n'pedal commuter series, particularly the larger one. It's quite versatile.
The rack attachment system can be hidden/ which makes it confortable as a messenger bag or backpack: you don't get spiky things stabbing you hips or back. And it has four strap attachments which means it can be configured as a whatever you like.
I had it for 4 years and is still going strong.

Thinks 15 miles in steady rain . . . nothing can match an ortlieb bag for durability and staying dry. Pannier racks can be tricky, make sure they don't interfere with disk brakes. Lightweight and flexible are better thank the chunky rigid ones which don't flex with the bike frame so crack sooner.
I like these http://www.halfords.com/cycling/bike-accessories/bike-pannier-racks/axiom-streamliner-road-deluxe-rear-pannier-rack

Other options are described here
http://road.cc/content/buyers-guide/206090-your-guide-racks-and-panniers-%E2%80%94-all-your-bike-luggage-possibilities-low

Planet X have a sale 18% off everything today, 16% off everything tomorrow, 14% the day after etc. sadly they don't sell ortlieb or axiom https://www.planetx.co.uk/c/q/accessories/bags-and-luggage

Tubus rack + Ortlieb back roller pannier

If you wanna go down the rucksack route then can definitelty vouch for the Ortlieb Commuter rucksacks, completely waterproof so no matter the weather can chuck everything in the bag and it'll all be fine, they're a bit expensive but the build quality and guarantee makes it worth it imo

For the price I really like my Timbuk2 deluxe messenger.