I'm a fan of the .06 if you're only going to have 1 rifle or your first. The recoil is manageable and the brass and availability is the greatest. close seconds are .308 and .270. All of them will kill elk, deer, antelope, pigs, etc. Your familiarity with and shooting it will provide the greatest accuracy. After having one and finding out what you like you might personalize one for a certain species of find something you like better.
It's like buying 40. later you decide a 60 is nice for exp trips since it hauls more. Then you buy a hilux for chores around the house your doing, then 80 or 100 for the wife and kids. Do you need all those, no. You can make the 40 work for everything. Other things may do better for specific things but in the long run it's tough to beat a 40 and it's always reliable. same with an .06 You may eventually decide on something else like a 300mag, 338, 7mm or something you just happen to like but it's always good to have that solid base to make/base your decisions on.
See you on the trail
Couple o' FJ40's, BJ70, PZJ77, UZJ100, TDI