TomJ said:
Among the major manufacturers, is there really a difference other than the amount you use?
Yes, there are differences in terms of metering characteristics (+/- .1 gr variance compared to .2+ gr), muzzle velocities you can achieve, how clean/dirty they burn, ability to produce lighter recoil yet accurate target loads, different amount/type of felt recoil/muzzle flip, accuracy at different load levels, cost per round, etc.
loading .38's and .45's ... looking for a recommendation
Differences in popular powders are covered in detail in this thread and it should help you with your powder purchase -
http://www.thehighroad.org/showthread.php?p=9890280#post9890280
For new reloaders, I usually recommend powders that are flexible to reload many calibers that can produce accuracy at lower powder charges as new reloaders usually don't load at near max/max load data and typically load at mid to high range load data. I also recommend powders that meter well (produce +/- .1 gr variance charge to charge) until techniques/skills can be developed to consistently meter larger flake powders like Unique.
The powders I prefer to recommend to new reloaders and popular with many reloaders are W231/HP-38/Bullseye/Red Dot/Promo as they can load many calibers and can produce accurate loads even when loaded light.
W231/HP-38/Bullseye meter very well and very popular for .38/45 loads.
Titegroup also meters well and produces accurate target loads and popular with match shooters but it often has very narrow load range (.3-.5 gr spread) so your start charge is already near max load. I do not recommend Titegroup to new reloaders until they are proficient with metering powder charges consistently using verified accurate scales. WST is also good for producing accurate target 9mm loads but there is no current published load data from Hodgdon.
Red Dot/Promo are large flake powders that meter with .2-.3 gr variance but if you load at mid range load data, even with the variance in powder charges can produce decent practice loads.
Many like Unique and like Red Dot/Promo, is a bulky large flake powder that fills the case well to not allow double charges (powder will spill over with most double charge ranges). But many reloaders have problem with consistently metering Unique.
Powders that burn slower than Unique/BE-86/Universal are favored by reloaders to produce higher velocity rounds. I consider BE-86 the modern Unique that meter well and it has produced some of most accurate loads for me in 9/40/45.
Here are some target pictures of 9/40/45 loads using BE-86/Promo/WST/Titegroup -
http://www.thehighroad.org/showthread.php?p=9924922#post9924922