Depends what you sort of events you mean & what you want out of them...
I personally (marketing freelancer) haven't found local networking events particularly fruitful in terms of business development. Too many sold traders who cannot afford me. However, I do know people that have found them useful not only for business development but also for developing a support network as it can be lonely freelancing etc.
I have a niche and have found that sector events much more useful in terms of contacts and 'being seen' etc.
Unfortunately I think the only way to find out what a network/event is like is to go. If possible don't pay any annual fees until you have sampled an event as I found they all have a different feel.
The best networking events are ones where other attendees have the same client base as you. So it depends what you are offering in terms of which events are best for you.
I don't market my business at the moment and haven't been networking for quite a while, but the best groups for me were ones with plenty of accountants, IFAs, IT people, basically any providers of business support to small business owners.
I'm a journalist and have made a few interesting contacts. It's a free event every month at a nice hotel. Good food, wine and a raffle. I quite enjoy it, but it is a very relaxed affair and sometimes, when you don't feel up to it, it can be boring.
I've been to a fair few networking events, most recently 300 Seconds in MediaCity. Advice I would give you is never pay for networking unless you have a guaranteed way to recoup the cost from business gained through it. Social media networking reaches so many people for free if done right, and at its heart networking is just talking to people. You do that every day without paying for the privilege. I'm part of a FB free business support group, started from MN. PM me if you want to join.