I just cashed out my 2nd check of $37 with inboxdollar. On the scale from 1-10, inboxdollar would get a 6 while Fusioncash would get a 4 on my vote if I have to make the comparison.
Inbox
Offers: there are many more offers, free or purchases than FC and sometimes the rewards are paid a little higher than FC
support: they have livechat, you can get help instantly while you would have to wait at least 3 days here at FC. Here is the tip to make sure of getting your credits at inbox. Write down the name and date of the offers you completed, contact livechat after 14 days of completion, rest assure you will get the credits 1-2 days after this contact.
payment: -$3 for first check, but they will give you right back $3 bonus just for continue to be a member, 2nd check will process weekly
surveys: if you are more of a survey taker, I wouldn't recommend inbox because they are just a middle man type of site. For every completed survey you took, they get paid 75% while you get only 25%.
FC
Offers: less offers, pay out less in some of the offers in reward
support: no live support and if you seek help for a completed offers (assuming you did everything correct) you did not get paid, rest assure that you won't get paid because the advertisers didn't pay at the time or never pay. I completed about 5 sign up offers here, but never get paid.
payment: monthly payment, no fee which is better than inbox, have paypal payment which is also better than inbox
surveys: better than inbox a little with the FC surveys, more daily surveys than inbox, but the rewards are just about the same with inbox, very low, but that's understandable, every middle man site would do this or they won't survive. If you are more of a survey takers, I would recommend FC over inbox if I have to make a choice between the two.
Other activities I like at FC are the 15 cents daily paid to click, posting forum bonus.
Note: this is just my honest opinions, just tell it based on my personal experience only, so don't slam me over this. I would love to hear your opinions also, whether it is FC or inbox better, but please point them out, so we could have better understanding. I read some previous posts and someone said FC or inbox better b/c he/she made more money at one site compared to the other without elaborate why.