Both are fine deer calibers. I've been shooting the same Savage .243 since the early 60's without ANY barrel issues. Don't be concerned about burning one up. You are correct about more factory ammo options and bullet options for the .243. With the newer Barnes TTSX and other X bullets you can reload even 80 and 85 gr. loads and be good for deer. The .257 isn't going to do anything for you that the .243 can't IMHO, so pick a rifle that fits you well and take your pick of calibers. If you think you might want something bigger, look at the .260 Rem or 7mm-08. Both cartridges, like the .243, are necked down .308 cases.
