Sput!
I advise extreme caution regarding both of the methods you mention.
Promoting an RPG is a very difficult task and to be successful it requires a lot of lateral thinking. The first issue depends on your venue of sales.
If you're "going to book" in the classic store-sales mode, then promoting to that distribution network becomes the priority. Print ads serve one, single, only purpose - to advertise to distributors and retailers that you are solvent. By all accounts they do not have any impact on the buying public. Even worse, if you don't have name-recognition with said distributors and retailers already, those ads will be ignored!
Store/book sales offer a conundrum: to be ordered, people want assurance that you are a strong seller, and you won't be sold anywhere unless you're ordered first. Gah! Even worse, they are often internet-phobic and perceive good internet-sales history as a threat, rather than as an indicator of future success.
If you're going to be selling PDFs or selling the book on-line, then you need to consider promoting to the role-playing on-line community in some
distinctive way. Unfortunately, banner-link ads are of dubious utility, and all input I've received from RPG-publishing-type people indicates that they do very badly. If you go with one, I suggest somewhere like RPG.net where people are already interested in the material.
Much more effective is a strong presence on internet forums (hello! waves) and getting the game's name on the various indexes, especially those which contain or even favor underground/small-press games. Unfortunately, one of the best things for Sorcerer was multiple links across dozens of sites, but times seemed to have changed a bit - and surfing from link page to link page isn't as common as it used to be. So now, it would be more important to get yourself reachable by Google via
many keywords.
I strongly suggest contacting Liz Fulda of the
Sphinx Group and getting a solid hour of advice from her. Not only will that be the best hour you spend in this side of the biz, but you can see whether she or someone she recommends can be hired as an agent, even on a temporary basis.
I've got more to say about all this (hoo, lots more) but that's a start, anyway.
Best,
Ron