All of the photo hosting sites will offer a free and a paid membership, with the paid membership offering you unlimited photo uploading ability. Here's some other things to take into consideration...
Some sites will resize your photos, automatically. Photobucket used to, though I don't know if they still do. Flickr does NOT, which is another primary reason I use it. It allows me to use it as a "cloud back up."
Some sites allow you to "right click disable" and disallow others from downloading your photos, some sites do not. Flockr does, which is another reason I use it.
Some sites make it difficult to share your photos with other people, requiring the other people to either have an account or an invite from you. Photobucket used to be that way thought I don't think they are any more.
Look at how easy each integrate with smart phones.
Also look at how easy it is to upload and to Bulk upload. Flickr offers a Flickr Uploader, which makes it very easy to bulk upload as many photos as I want, at a time.
If it's of any interest to you, also look at how each site allows you to synch them with social media sites, such as Facebook, Twitter, etc.
If you're happy with your host site, as long as it's not a whole lot more expensive than others, it may be worth keeping it. Otherwise, you're looking at having to upload those photos, all over again, to a new hosting site.
