You got two? God I hate you
I've been using serebii for that.
In terms of stats nothing changes really. Every pokemon has a base stat, as you know, and a pokemon will always get its base stats regardless of when it was evolved - EV's IV's and all of that are carried over through the evolution so the same benefits are carried over too. But, of course, Fully evolved pokemons stats > NFE stats
The benefits of getting the 1st stage pokemon are that A) it's easier to evolve than to breed - pokedex filled quicker. B) holding off on evolution means that pokemon can learn certain moves quicker C) easier to train to a desired level. So, I always get the first evo where possible .
Hope I answered your question in a round about way lol.