Turbo Engines are HIGH mantinence. You will always be tweaking something here or there. Now, a B series will be more reliable over all and much easier to deal with when things go wrong. Since you already have the D series though, it might be work tuning. A turbo isnt cheap, I've heard that there are some good D series kits available and some comming out soon. If you plan on running this on an unmodified block just be careful how you boost. Make sure all your complementary systems are stong, a powerful engine is only as strong as its weakes link.
If you get a B series, dont let people tell you its just 3300 (using B18c1 as example). You dont NEED to get mounts, but you'll regret it later if you have an older car. You will need someone to install it(though its better experience to do it yourself, if you have a shop do it and something goes wrong, its their problem not yours and thats nice.), then you'll want to get all the bolt on's(most of which are useless if you later go turbo), and of course a good clutch. But you will be "quick" and have a very reliable and fun car to drive.
If you go turbo, there are many things you'll buy that are usable on different engines...like the turbo, some piping, intercooler, injectors, fuel system, ignistion, etc. If you later buy a B series swap, a lot of you stuff will transfer easily. In the mean time you will be faster than the Standard B series swap, most likely.
There is far more information and if you have any questions PM or AIM me as im finishing up my D sereis turbo and have worked with others on B series and various nissan projects(helps to have diversity when dealing with turbos.)