My advice --
If you're doing between 100-150k/year, concentrate IMMEDIATELY on one program and stick with it thru the end. At least for the two biggies -- AA/UA -- the top tier is almost like flying an entirely different airline in terms of the service you get.
As for which program you go with, you need to decide what's most important to you. Things to take into account --
(a) Route Network. How many places does the airline fly, and how many stops will it take you to get to them. As far as i know, CMH isn't a hub for any airline you'd want to fly on a regular basis, so no one has a decisive advantage here. But consider what cities each airline will have you connecting to.
(b) International travel. If you plan a lot of international travel, you'll probably want to stick with AA or UA, because of Star Alliance and One world. These two look similar at first blush, but there are a LOT of subtle differences. With AA/One World, you get your 100% mileage bonus on the partner airlines, while with UA/*A, you get the base miles, but not the bonus.
(c) Ease of domestic upgrades. At top tier US/CO/NW, you'll get unlimited domestic upgrades (availability permitting) without paying anything. At AA/UA, you get comped for 2,000 miles of travel for every 10,000 miles you fly. But it gets more interesting than that. DL, for instance, won't let you upgrade from their cheaper fares. AA and UA will let you confirm a companion upgrade at the sime time you are upgraded in advance of the flight, while CO/NW will do it only immediately before departure if there are still seats left. DL never lets you use your status to upgrade a companion.
(d) International Upgrades. Here there are a lot of differences. Different airlines each have different rules for which fares can and can not be upgraded. AA tends to be the most liberal (almost any fare, even some that won't earn you any miles), while DL is the most restrictive (only Y/B/M can be upgraded internationally). Everyone else falls inbetween AA and DL. But there are more differences, too. For instance, CO won't let you confirm an int'l upgrade until 30 days prior to departure.
(e) Bonus miles. At top tier, most airlines will give you 100% bonus miles. CO gives you 125% bonus miles.
(f) Top tier benefits. Most airlines offer an extra "kicker" on top of the incrimental benefits for their top tier fliers. On AA, the kickers are comped domestic upgrades on Y/B fares, access to the EXP desk (which can and does waive fees), and 8 VIPOW's (which can be used for a one-way upgrade systemwide on AA). At UA, you get 6 systemwide upgrades, and access to the 1K desk, which is nice, but isn't at the level of AA's EXP desk. At DL, you get unlimited domestic upgrades (except on L/U fares), and 6 SWU's per year, but you're handled by the same desk that handles the Gold Medallions, and you won't get fees waived. DL and CO will give you complimentary lounge access.
(g) Fleet. This can be a huge difference. AA flies tons of MD-80's, which a lot of people don't like. UA still has lots of crappy old 727's. CO flies their long-haul domestic flights in 737's. DL packs their new planes like sardines in coach.
(h) Premium Products. If your going to do int'l travel, and your company will pay for you to be in Biz Class, do you want to be able to upgrade to first? Among the domestic airlines, only AA and UA (and sometimes US) offer an int'l FC product. But DL and CO have them beat in when it comes to just Biz class, so if you'll be upgrading from Y to J, CO or DL might be a better choice.
There are a whole host of other considerations, but I hope this helps.
Good luck.
