The Accuguard is a Vanguard series 2, just a specific model in the Vanguard 2 line. Pretty much any new(er) Vanguard you find will be a series 2 and carry a three shot, .99” or less accuracy guarantee. Choosing an Accuguard over a Wilderness, or it over say a Vanguard SS, just comes down to personal preference features you are looking for. I know around here the newer Vanguard First Lite has been very popular here lately.
As far as ammo goes, the correct answer is whichever one your rifle shoots the best. There isn’t a factory produced .257WBY ammunition that isn’t going to be instant death to a whitetail. Personally, I shoot three different 257s regularly and in two of them I run the 110 grain Nosler Accubonds and in the other the 100grain Barnes TTSX. But the lighter Barnes load, the Nosler BT and Partition, either of the Hornady loads, and even the WBY Select 100 grain Norma’s are going to anchor a whitetail DRT.
If you go the Nosler Accubond route, you can get the ones loaded directly from Nosler for about $20-25 cheaper than the slightly hotter loaded ones directly from WBY. The majority of fellas around here run the 100 grain Barnes and swear by them.
Hope that helped a little. Good luck and welcome to Weatherby Nation!