I'm not a Realtor or anything just giving my 2 cents as I have grown up in Houston/Katy.
Katy is for sure for families and less focused on young professionals. If you were to live in Katy and worked downtown you are looking at a 30-35 minute commute with no traffic, or with morning workday traffic upwards of an hour. Katy is about 15 miles West of Houston. Most professionals in Katy take Metro (Houston Bus System) to get to downtown. They can ride in the HOV (2+ minimum most hours of the day) lanes and usually get you there pretty quick and most companies will pay for this.
If you are in to the younger night life you want to be inside the loop. Inside beltway 8 as a minimum, preferably inside 610. Night life wise their are 2 main areas, Midtown (south of downtown) and Washington Ave for the bar/club scenes. There are a few upscale bars in Upper Kirby (Just North of 610 on Kirby), and some local music scene type bars in the Heights people will go to. Areas close to these areas are the Heights (North of I-10, West of 45, southeast of 610), Galleria/uptown (West of 610, North of 59, South of 10), Rice Military (South of I-10, North of Memorial, east of 610), and Montrose/Neartown (Just west of midtown, generally considered to be a center for the LGBT community). Most recent grads/ young couples will live in these areas as for the most part rent could be affordable if you look at the right places. Before you start looking you need to decide if you would like to live in a midrise (If you have a small dog), a condo/townhome (2 bedrooms will rent about the 1200+ range), or will try a home (your best bet would be the heights for this). All of the places I mentioned are no more than 15 minutes to night life. Shopping wise one of the more famous places will be the Galleria which is located in the uptown area (Area where 610 and 59 intersect on the west side of 610). Again all of these places I mentioned will be about 20 minutes tops to the Galleria.
Hope this helps.