Travelguard.com is my go to because it waives the pre-existing condition exclusion when purchased close to your booking date. No matter who you choose I recommend reading the actual policy before buying. Most sites will have a link to the policy somewhere on their site but you have to dig for it. Read to make sure it will cover what's important to you. If you don't understand something call and ask. If I recall, travelguard has the link to the policy language when you quote the price.