What Kind of Oil?

Hey I just bought an 04 Accord EX V6, I'm clueless as to what type of engine oil to use in it. I've been told Mobil 1, Syntec, etc... but then today while attempting to buy some Mobil 1 the guy at AutoZone tried to tell me Mobil 1 will "ruin the engine, so that you can never use anything but Mobil 1." Any advice would be appreciated, I just don't wanna get screwed or use something that's not necessary. Also, any recommendations on iridium plugs, are they worth it? If so, what brand(s)? Thanks!!

as i understand there is a myth of once u go synthetic u cant go back, which proved to be false, but i use mobil 1 synthetic 5w-30 in my 2000 accord EX V6, and it might be my imagination but the engine performs alot smoother. I dont know if the mobil 1 synthetic might mess up the newer accords, but i dont know why they would as long as you got the right SAE rating and the highest API rating
I also heard spark plugs don't really matter. I have the Bosch Platinum +4...which i regret getting because it was the price of iridiums, but not the quality of them. platinum lasts long, but not a great conductor, (the other metal, i forgot) is a great conductor but doesnt last long, and the iridiums are supposed to have the best of both worlds. Iridiums run for a good 6-7 bucks a piece. If you're looking to save a little bit of money, i heard the NGK sparks are a good brand to stick with. Doesnt really matter what kind of spark plugs u have, if any gain and loss it'll be too small to notice

BTW don't quote me on all of that, 98% is word of mouth...