Dave:
I've been on both the Spree and the Fling in the FG, total of 3 trips so far (got weathered out of our 4th and 5th both last year) between 2005 and 2007. Of the two I "preferred" the Spree, but it was a fairly minor difference based on the Spree having a slight remodel with a dive-deck freshwater shower that was really convenient, that and Frank and Melanie somehow seem more 'personal'. None of which is to say anything bad about the Fling - just didn't really seem to get to know the captain as socially, but the DMs and mess crew were all great. And anyway the Spree is no longer an option for the FG, by May of this year.
Don't worry about getting buddied up; whichever shop you sign with should handle that - usually on the Fling there's 2 to 3 shops that "resell" the seats for the FG trip, so they have 9 - 15 positions per trip, and their "trip leader" DM can always be your buddy if all else fails and they can't find you another singleton or add you to a 2fer to make a triple. I'd recommend Tom's Dive and Scuba in Austin, only because I've bought Fling trips thru them before and had no troubles.
If there's any way you could make it down the weekend earlier, my wife and I are scheduled for the Memorial day trip, which is Friday departure for Sat/Sun/Mon diving. The 3 day trips are a bit better value in terms of dives for the cost, but don't flinch away from a 2 dayer especially if you're as close as Houston. May is still a bit dicey weather-wise - trips get the go/no-go call at noon - 1pm or so on date of departure, but if you're right there in Houston you're only an hour or so drive away. Its a bit tighter for me leaving from DFW - we usually get a jump on the call by an hour or so just in case of bad traffic on the way down (and once never got the darn call, since they left the no-go message on my WORK phone line, but that was the dive shop's issue not the Fling's fault specifically). So make sure whoever you book with has a good mobile contact number.
I'll probably flesh this out later tonight with more details but here's a few top of the head (and as much as I can get away with posting from work) perceptions:
1. Dive-dive-dive! Don't miss a single one if you can help it (barring exhaustion, cold, deco trouble, or blockage, of course...safety first). Basically don't skip one just because "its the same mooring" or "just wanna work on my pics".
2. Diving is spectacular considering it's just a skip off the TX coast. VERY good coral coverage upward of 70% in many places. But it may be different than you're used to - depth and winter temps mean no soft corals at all, only stony corals and sponges. (Stetson being a clay bank generally has only sponges). Fish life is plentiful, varied, to include a chance of pelagics. I've only personally seen a couple of reef sharks, but tigers and silkies have been spotted, hammers in the earlier spring. I've also seen eagle, southern sting, and manta rays, and mobulas and whalesharks are also possible. At least one large turtle sighting is practically guaranteed, as are a large grouper or two (largest I've seen was about 3 foot, but hear there may be bigger ranging into the gardens). Rig dives are cool - angelfish as big as platters and schools of sportfish (jacks, ambers, etc) in great viz, plus all the tiny stuff on the rig legs.
3. Viz overall is good to excellent - 50 foot is the worst I've seen at depth - unless the current kicks up at Stetson - and 80 is probably the best I've seen. Not likely to hit a gin-clear 100 like the Bahamas though, but this is definitely not freshwater diving.
4. There can be current, and it can be quite significant, especially crossing thru from safety stop to surface levels. You and your buddy are navigating your own dives!! This is not a guided tour, so take nav seriously, or you'll be riding the dinghy of shame. There can be high swells making egress to the ladder a bit sporty sometimes. Oh, and the boat crossing from port and back can get rough - plan accordingly if you have motion sickness. (Fortunately I don't.)
5. Nitrox is HIGHLY recommended to get the most out of your dive time. If you want to dive a steel tank they have them but usually upcharge...check with the dive shop for the details.
6. Highly recommend downloading the "FAQ" from the Fling's website and reading it thoroughly. They are NOT kidding about their dive rules (130 fsw max first dive, 100 thereafter, no deco, out of air = SIT OUT THE TRIP). I know the Spree recognized solo divers with proper rig and cert, not sure about the Fling.
7. "Cabins" are incredibly spartan - basically a bunk and a curtain so you can change without mooning the hall. Don't worry, you won't spend any time downstairs that you aren't asleep or in your bunk reading. There's plenty of outlets at the galley tables for processing, battery recharge, etc and someone's always up there. The mess crew generally are quite pleasant and love to chitchat or will leave you alone if you want to bury your face in a book.
8. Only really "weird" thing about the trip to me is the boarding cattle-call. Basically you'll fill out all papers at the dock (TAKE REPELLANT - the mosquitos on the river are the size of small dogs, and twice as viscious!!), then when they give you the 'all aboard' brief and say go for it, you either book for a bunk claim (drop your clothes bag on one) or for a spot along the dive benches (reserve with gear bag). Me, I'd prefer getting a good dive spot (avoid the middle row under the wetsuit hangings) and just grab one of the bunks under the 'stairs' vs. fighting for a cabin - they're actually quite comfortable unless you're extremely light/noise sensitive when sleeping.
9. Remember you're 100 miles from shore. Bring backup o-rings, straps, batteries. For clothing keep it simple - shorts/t-shirts/tevas/skivvies, maybe a sweatshirt or warm hat for the spring if you chill easily (they do keep the belowdecks pretty cool as well).
Botom line, I highly recommend it. For about $500 for meals/bunk/7 dives for a 2-day trip, or $740 for a 3-day (nitrox included) w/ 11 dives, the price is pretty reasonable as compared to the usual $80-100 for 2-dives at nearer-to-shore locations. And it really is an impressive dive locale, with a couple hundred acres overall in sport diving range that's extremely lively and healthy. Of course I haven't seen it since this past fall's hurricane season, but reports I heard were that there was some sanding-over and a few of the larger (VW bus sized) brain coral heads had tipped where they were all bioeroded underneath, but that's been obviously going on there for centuries.