a mutt....
always had good luck with em , and theres tons of cross breeds and personalitys....
give em a good home and stray mutts will be with you forever , also normaly pretty street savy. if i was going to take a dog with me i would probably go with a terrier or other smaller smart dog.... my terrier is smart and quiet and takes commands really well and is a heck of a little work dog. she barks to tell me whos comming down my drive way "3 barks its the post office lady with biscuits) and uncontrolled is probably some random person she doesnt know. 2 barks and its one of my family...also goes after mice and birds and rats, snakes and the kind.

.... you also are going to be a lot more scared of the owner then my dog.

but honestly its not the breed of the dog i think thats going to matter if your traveling the world on your own two feet... youll have to train them at command , how to stick very close to you. to only take food and water when you can say its ok.... there is a lotta stuff out there they shouldnt eat/drink. and plenty of people throw out tainted food.... and have to stop and heal at command...

things i think a 1+ year old stray would help with. of course you will have to accomidate them as well.

even better if there a little larger so they can take there own pack.