As has been suggested, the choice of scale is a very personal one. There are a lot of factors to concider, and you've only scratched the surface of them.
Size is important. HO scale offers one the ability to model a very detailed scene in a reasonable space. Smaller details are able to be modeled and their inclusion can be appreciated. N scale however, has a diminished detail threshold. Those tiny details are lost. What you gain though is the vastness of the real world! You can model scenery that really dwarfs the trans. Trains that are closer to a prototypical length, and cityscapes and mountains that tower over them. I'm not saying that an N scale model cannot look very detailed though.....it can! (Just check out this fine example of N scale modeling:
http://i83.photobucket.com/albums/j319/pcarrell/What Scale/WSII78.jpg)
It's true that HO scale has much more then any other scale available off the shelves, but N scale is closing that gap all the time! Still, the fact remains, HO has a lot more available off the shelf and so it's probably the easiest scale to get started in from that standpoint. I'm not saying that it's easy to master or doesn't require skill, not at all. I'm just saying that if you want to run a Heisler locomotive for example, in HO you'll have several choices of manufacturers, whereas in N scale you're going to be honing your scratchbuilding skills.
As far as cost goes, there isn't a lot of difference between N scale and HO these days. The real conciderations are those of a physical limitation, such as poorer eyesight or shakey hands (N scale parts can be pretty small, though an optivisor can help) and the astetic differences (detail vs. vastness).
One last consideration is sound. HO loco's can virtually all have sound. They either come that way or there's room to add it. N scale is just beginning to get sound. It can be had from the factories in a few loco's, but for the most part it's still coming. There are a lot of loco's that it would be difficult to add sound to because of space conciderations too. It's not a deal killer, but something worth concidering.
I'm an N scaler. Switched from HO to N back in the 80's and haven't looked back. I love N scale and until my eyesight prevents me from modeling it, I'll probably stick with it.
My recommendation to you?
Go to a local hobby shop. Take a look at models in all the scales you're interested in. Get your hands on them. Look at the building and bridge kits, check out the scenery materials. One scale will "speak" to you. It'll stand out as the right one for you.
Thats your scale!