I'd try a forum. If done correctly, you are well on your way. For one thing, you don't need to provide content; your members do that themselves. I think it's best - if done well.
Forums are the way to go . BUT - as you can see it's bit but - the competition in the forum domain is INSANE . This niche has been over used and over abused . There are big webmaster out there that won't hesitate to blast you to bits if you get some of their users .
Forums could be more profitable.. but I think blogs are easier to build and maintain. Blogs are also easier to rank on search engines. So, if you are trying to build a dating community I would say build a forum and if you don't want to build a community then use blog.
I think blogs are better for this niche in particular. You can give organized advice and this is something people browsing on such topic are looking for. And you can also personalize it to the point where surfers remember it easily.
I agree with the blog first, forum second route. It's a lot easier to get a blog off of the ground. Plus, once you start building a serious following and roll out the forum, you'll have all of your followers from your blog that are now potential users of your forum, too.
If you are really interested in building a serious and long-term business, I would HIGHLY RECOMMEND to start off with a blog. It's easy to install and you can build up good reputation and you have lots of methods to monetize your blog...promoting other people's products, Google AdSense and other programs. This is the first way...later on you have the opportunity to create own products and sell it to your people...so I would recommend to mix blog and list-building together and you will have a killer sauce that will generate tons of cash every single month. The Rhodes Brothers are doing this and they are making a killing with it...believe me.