Typhlosion is probably better it has access to a bigger movepool and comes with egg moves from the vendor. The only reason you should keep arcanine is as a revenge killer with extreme speed but with a sucker punch decidue It's not really necessary. Typhlosion is faster and hits harder than arcanine because the moves it can learn have a higher base power than your current arcanine's, but typhlosion is a little less bulky than arcanine. On the other hand arcanine's higher BST might seem better but I'd give the slot to Typhlosion overall. If you do choose typhlosion try an eruption for when typhlosion is at higher health flamethrower for more consistant damage sunny day to boost your fire moves power and solar beam to take care of water types. Solar beam takes 1 turn to charge in harsh sunlight.