As Jason mentioned I did a good bit of research before updating my solar heater last spring (old solar heater came down when the old roof was replaced last year). I will try not to get into too much detail on this reply as there is still a lot of information about your potential install that is not covered, like intended mounting location for panels, local weather tendencies, etc. Therefore for now I will just include some general observations, along with a few personal opinions.
1, There is no one perfect solar panel for everyone, for example a fairly stiff flat panel like the Techo-Solis panels I ended up going with may work better when installed on a surface that has good support, but is not entirely flat (mine is installed on an R panel metal roof with small 1/4 inch ridges every few inches and 1 inch high ridges every foot. Where a more flexible individual tube and header design might have problems with sagging, trapped air, gurgling, etc.
2, Better costs more up to a point, after a certain point the added cost seems to mostly be going toward paying for a longer warranty, with little or nothing going towards a better longer lasting panel.
3, Read the warranty carefully, many may look good at first glance, but upon careful review may be nearly worthless, often freight is not included in the warranty, and for the more rigid panels that must be shipped truck freight, this can add up to a substantial fraction of the price of the panel as the cost to ship 1 panel, is likely to be nearly the same as shipping a dozen. Also some of the warranties are written so as to be 10 or even 20 years prorated, so that you pay 1/2 the retail price of the panel for replacements after the first 3-5 years, note this is not 1/2 the price you paid, as that is often already discounted off the retail price by 20-30%.
4, Some manufacturers tend to sell nearly exclusively inside their dealer / installer networks (Fafco and Heliocol come to mind, although Fafco does sell some DIY kits on their lower end products) Also some will not warrant DIY installs.
5, Many manufacturers play the Private Label game, where they offer the exact same panel under different trade names and under different terms, so you may find Brand X sells its panel exclusively through a dealer network with say a 12 year warranty, but also sells it to a 3rd party private labeller who sells the same panel to independent installers and DIY'ers. This 3rd party private labeller takes over warranty issues, and may often provide a shorter 4-5 year warranty while selling the panel at a fraction of the "name brand" price. A couple of examples here are Aqua Therm and Elm Distribution (if you look carefully you will note Elm's installation manual is the Aqua Therm manual, depending on where you download it the manual may or may not have the Aqua Therm logo removed. You can also note that Solar Direct's inground pool panel appears to be the same as the 1.5 inch header version of the Techno Solis panel (looks identical, plus same exact specification measurements for all dimensions, and weights).
6, If you do use an installer make sure they are a good one, there are all sorts of examples of poor and incorrect installations on the net, just because they have installed a lot of panels does not mean they did them right. One message thread I recall on here from earlier this year featured a photo of one of the exclusive installer network installed panels (heliocol?) pulling the header pipes up off the shingles, a close view of the photo shows the installer used the footer mounts on the header and the header mounts on the footer.
7, Don't get too concerned about panel efficiency, most of the better panels are going to be close to each other (within 10%), and your house is not the same as laboratory conditions. For example a rippled panel design like the Aqua Therm Eco Sun panel may perform better in ideal south facing windless installation , but may loose more heat to wind than a flat panel like the Techno Solis panels, or may self shade if angled too far east or west.
8, Sizing solar panels is partly an art, partly a science, but also involves a question of expectations, A person that enjoys swimming in the afternoon or evenings(after the solar panels may have boosted water temperature 2-3 degrees from its over night morning low) in an 83 degree pool and only wants a slightly extended swim season may be happy with a panel array that equals 50% of their pool surface area, yet another person that wants to swim in 90 degree water first thing in the morning 9 months out of the year may not be satisfied with a 100% surface sized panel array. Local expert knowledge may help here, as most of the available national solar statistics are geared towards photo voltatic (electric generating) solar panels, and don't take into account local seasonal weather patterns. For example an area that tends to suffer from lots of overcast at the end of the traditional swim season followed by lots of sunlight the next (cooler) month might never be able to regain heat lost during those cloudy days.
I hope this has been of some help, tell us more about your situation and goals and we can help more
Ike