What method is better dsound.dll or injection?
Well basically, injection is the best method for internal menus. Most drag and drop menus using dsound.dll get detected quickly compared to ones injected.
How to make it undetected
For it to undetected, it needs to use undetected natives and the best source to use i would say would be sudomod and you'd have to use CrossMapping for 1.40 to update the source. It also doesn't matter if it uses Direct Calls or a Native Involker. Just Direct calls is slightly safer but harder to program in. For dropping money and other things it would need to hook the events REQUEST_PICKUP, REPORT_MYSELF, and REPORT_CASH_SPAWN to prevent the reporting of yourself when spawning the money, picking it up etc.
Which is safer, Free menus or Paid
Now about the paid menus to free menus. Which one is safer? Well, it all depends really. Most paid menus are just re-skins of the Galaxy Menu which is, quite frankly, shit; they almost get detected quickly and are almost never trusted due to what it's based after. I can't say what paid menus are good but I know of a few really good and safe ones. Now the reason why people say paid menus are safer because a lot of people don't buy it so it's not being abused by people and not bringing attention to it, compared to free menus, where it's open to everyone and can be abused to whoever. The best free menus at the moment would be external being as some of the greatest minds in GTA modding have gone over to making paid menus. It's quite sad really.
Brief summery
I would say at the moment, the best to use would be external menus and those would "Mike's external menu" or "subVersion GTA:O External Hack". Their both free and are the safest to use. However subVersion GTA:O External Hack is not located on this forum so you have to search for it.
Hope this helped