A good install matters more than brand. Get a couple quotes, and pick a brand that the local service folk can actually get parts for in a reasonable time period.
being in Texas, find someone who actually knows how to do flex duct - i've seen plenty of horrible octopus installs that leak half the air into the attic or are kinked and don't deliver properly. a good install looks tidy.
because you rarely need heat, and it doesn't get cold often, I'd suggest a heat pump unless you already have gas service and want gas. you really don't need a furnace.
it's common for people to look at what you have, and sell you the next size up as a CYA to make sure you stay cool. this isn't a good thing - a properly sized system is what you want. if your system is too big for your home it won't pull the humidity out properly and you'll be cool and damp. dry and cool is much more pleasant (and feels cooler).
if you're in a particularly humid area, consider a whole house dehumidifier.
I'd also suggest you get at least a two stage system (not sized larger than a single stage would be). this gets you a more efficient system that runs longer, more quietly, and dries better - then it can kick up to full power for the hot days. typically stage 1 is 66%-70% of the "ton" rating. would you want a car with a one position gas pedal? No? then why would you want A/C with one speed?
and as always - remember: you pay for insulation once, you pay EVERY TIME you run the AC! upgrade your insulation/windows and enjoy lower utility bills for years, plus you can save money by not installing as big an HVAC system.
