OP, here's my personal thoughts on suits for interviews. First, realize that if you are accepted you will wear this same suit and its brothers for many years to come, irregardless of specialty. Second, never ever buy a suit online unless you recently (as in the last 6 months) bought a suit and you remember every one of your intimate sizing details (many men know their jacket size and their pants size but might not know their sleeve length, how much to bring it in or take it out in the back, inner hem length, etc until you have a tailor work with you and many find this helpful to accomplish every suit purchase). Third, shop around some unless you have a personal preference for a particular store, i.e. mine is Men's Wearhouse because of their constant professionalism, knowledge about suits for particular occasions, wide range of selection for all occasions, and the friendliness of their salespeople. I have shopped other stores as well, but in my opinion the Men's Wearhouse is the absolute best. (an added benefit is that they have a free club for accruing points from purchases that will give you coupons, etc toward future purchases and for me this will come in very handy over the years)
Case in point, I recently acquired a suit at Men's Wearhouse as a result of getting married and using the Men's Wearhouse for my groom party which gave me a coupon for up to $450 for a suit. They were professional in the knowledge of knowing which suits are best for professional interviews down to the minutest point. Overall, you want a black or navy suit for this occasion with a tie that doesn't contain a lot of designs that are going to detract from what you are saying during your interview (I settled on a red tie with stripes here). I own two other suits in addition to this suit (one black and one tan) that I will be using for interviews, which I bought at Kohl's. In my personal opinion, my most recent suit not only fits me the best due to recent tailoring and fitting but it looks outstanding. I was honestly able to spend around $200 including a new tie, tie chain and the tailoring. Also, they do a top notch job in presenting multiple looks with the one suit, which I think is important especially in the long run (after interviews). In addition to all of this, I have used all of my suits recently in the last six months due to interviews for letters as well as my wife undergoing the USCIS process for permanent residency. Of the three suits, the suit that I most recently acquired offers me the absolute best fit because it was tailored to me by a professional tailor (hard to get when you are buying online). When you're buying your first suit, it is ok to ask for help from knowledgeable people and to try on multiple brands, multiple styles, etc all before deciding which suit is the best. Even if you live in the middle of nowhere, buying a suit is an imperative trip to the closest shopping mecca to shop for a fantastic suit for you. Someone has already mentioned a slim fit suit, but this might not fit YOU the best but of course you won't know until you try it on. Some look fantastic in a design like this, others look absolutely horrid when they wear this style of a suit. I hope my anecdotal story helps and good luck with acquiring your first suit.