As far as the public is concerned, neither one will box you in. So, by all means, start with the memoir. It will give you a solid financial base, a cushion to fall back on when future novel sales slow to a trickle, and name recognition. All this is assuming that "Kari" is a pen name and that the real byline you're going to use rhymes with Odell Ohama. If that's true, then you can't miss!
Seriously, memoirs sell poorly. Period. That's the sad reality of it all. Unless you have a HUGE name and are actually in the news cycle every night, a recognizable name alone won't pull its weight, as most publishers have learned. The name has to belong to someone interesting, lovable (forget it, I'm not in the running), controversial, and responsible for important breaking news on a nearly daily basis. Anyone else, and you won't find a publisher within this universe who will take a chance on it.
Since I'm guessing that your goal is most likely to begin writing more "fiction novels" (please do me a favor and research "novels," "fiction," and why all novels are fiction whether or not you specify so), why not go for that from the start?
One suggestion, though. Don't restrict yourself as a writer to basing your novel loosely on your own life. That's a mistake far too many fledgling writers make in their work, and it's one that's far too confining a corner for any writer to paint himself into. You can begin your novel with a memorable personal incident or experience, if that seems to work. But, from there, let it all loose. Let the creative juices flow. Allow your main character's story to develop. Grab pieces of the lives of other interesting people you know or other characters you've discovered within fiction or in history.
For example: Are you really forty-five and married with five kids and two grandkids? Why not be 25, widowed, independently wealthy, and with a charge of bigamy hanging over your head? See what I mean? That last possibility, one can only hope, is a far stretch from even a loosely interpreted summary of your life. But it's right in keeping with something that will catch and hold a reader's attention. If your goal is to become a self-sustaining novel writer (See? I didn't go anywhere near "fiction novel"), you need all the creative help your brain can give you.
Always ask, as you plod along, "But what if …? But what if …?" And don't be afraid to explore whatever answers you dig up. That's what creative writing is all about, whether fiction or not. And it's certainly what helps to set gripping fiction apart from mundane, ho-hum summer reads.
Not something you asked for, I know, but definitely something you should keep in mind while penning that next Great American Novel. And, remember, I'll be pulling for you.
D. J. Herda is author of the new eBook series of writing advice, About Writing Right, available at Amazon and at fine booksellers everywhere.