Personal Observations and advice, based on the AVOID GRIT theme:
1. Self-serve high power hose, foaming brush, coin operated. These are fine if you don't mind drying off afterwards, scrubbing the mats at home, and AVOID AT ALL COSTS the brush. I have watched pickups coated in mud use the brush, and you just know there is grit in that thing just waitiing to carve your clearcoat. You will not have time to get the bugs off the front unless you pump huge $$ of coins.
2. Drive thru spinning plastic dervish thing. These, as stated above, can carry grit from somebody else to you. They miss lots of areas, damage aerials and mirrors, and are often out of various soaps and "waxes" without warning. Anytime a business has 5 or more signs saying they will not pay for damage, leave.
3. New multi-head high power hose drive thru. I like these for routine washes since they don't have the grit problem- at least if the filtration system get out all the sand.
4. Hand wash places. Over-priced and require a lot of monitoring to make sure they don't cut corners. OK if you need it pretty clean and lack time.
5. Hand wash at home with a hose and bucket. The best, but its hard work and takes time.
6. Mr Clean hose attachment. My mom LOVES this for her PT Cruiser showcar, as it leaves no rinsewater spots. I have not tried it.
I prefer to CAREFULLY REMOVE BUGS and road tar with the mildest soap and a fingernail. This avoids grinding grit into clearcoat by scrubbing. I ALWAYS apply a new coat of NuFinish to the front bonnet, bumper, and lenses where the bugs are the worst- it makes popping them off easier.
Always wash with carwash soap (not dishwasher liquid) and take your time, rinsing off as mucg sand as possible before starting in with the rag or sponge. Work from the top down, so the dirtiest(grittiest) areas get washed last and no grit is carried up the side of the car.
Use lots of warm water and a big bucket so teh grit falls to the bottom off your sponge.
Be wary of bird doo. It contains grit and can act as an abrasive if scubbed.