Haven't done swan on 9.0 (yet). Setting up on your side should not be too bad. There is a learning curve to it, but if you can get a server up and running with tables, you should be able to figure it out.
You mentioned several Windows clients that will need access. Based upon experience, your long term problem will be there. Of course I don't know about your specific situation, but in general any time you talk about Windows users in a group of more than 3 or so, there is at least one that should not be allowed to own a computer. The IPSec connection can be a bear to get going the first couple of times, almost impossible without someone on the other end that has a clue. Maintaining the configuration can have the same problems.
PPTP is much easier to deal with both initially and from a maintenance standpoint. The Windows pptp client is relativly mature. Most users seem to be able to deal with it much better than the alternative. Configuration seems to require less repair over the long term.
There are times that IPSec is a better alternative. Main point in it's favor is the encription involved, but if you use preshared keys even that is somewhat questionable. If you use a CA, the other can of worms gets bigger.
Short version, if you really really need the extra encryption, go for the IPSec route and buy some extra asprin. Otherwise, (Windows clients + Windows users) = pptp, in my opinion, thus the link to poptop.