ismenie, a couple of points:
1. I don't think my first response to you was particularly clear. Let me try again: Being a member of several programs is not bad at all. BUT: Splitting your limited travel between several programs is not very good, because when you do that you never gain the true benefits of an FFP loyalty program, because they tend to compound. You need to figure out your ideal program, and try to stick with that airline or airline alliance on all travel occasions, unless the purchase price of a competitor is significantly lower (like 20% or more lower).
2. OK, JFK and 8 trips a year: good info to start. But as Open Jaw asked, to where do you travel? Domestic vs International? Coast to coast or more local? This will make a difference, let me show you how. Let's assume you travel almost all of that domestically. Let's pick just one scenario and see what can be done if you pick a good program and stick with it. In this scenario, I will assume that your eight trips per year are long flights to the west coast. It's just an example to show you the potential. I will assume a 2500 mile one way leg, which is about the distance from JFK to LAX, and we will pick American AAdvantage and the One World Alliance as your FFP, simply because it is the program with which I am most familiar.
JFK to West Coast = 2500 miles, round trip 5000. Multiply that times 8 trips = 40K miles for the year. Now, if you spread this over three airlines, at the end of the year you will not achieve elite status in any of them, and you won't have enough earned miles for a round trip ticket on anywhere. But if all of this travel were on AA, you would easily obtain the first elite tier (Gold) and you would have enough miles for at least one round trip domestic reward trip.
But that is just to start! Since you qualified Elite Gold after about the first leg in your sixth trip, you will get a 25% bonus in earned miles, which will get you closer to two free domestic trips with judicious use of points! You will also get 500 mile upgrade "stickers", priority check in and boarding, and several waived fees. People underestimate the value of this lowly Gold elite status, but it is worth it!
It gets better: Maybe AA restarts their Double Elite Qualifying Miles. Lets say you manuever three of your trips into the AA "DEQM" window. Now instead of only about 40K elite qualifying miles, you will get 55K elite miles, which qualifies you for AA's Elite Platinum status. Now you get a 100% earned mileage bonus on all of your travel, and maybe you are close to THREE domestic reward round trips shortly into your second year, you get more 500 mile upgrade stickers, you have even higher upgrade likelyhood, and several other fine benefits.
But wait, there's more! Maybe you get a credit card with a generous sign up bonuse, like the Citi AAdvantage Platinum MC, and you get 25K free miles. We are darn close to four free domestic trips. (I'm using the AA Mile Saaver rate of 12.5K per direction). And you also signed up for the SPG AmEx, earning you another 25K miles after, part of it for initial sign up, part of that after spending $15K in six months. You break the code and start using this card for everything, including recurring automatic bills like phone bills, utilities etc. You earn, effectively, a fabulous 1.25 per dollar spent on this card. In the first year lets say you spend $30K on this card, being careful to pay it off every month. Now were are we? I'm gonna tell you. :
You only flew 40K miles. In your split out programs you would get very little. But because you stuck with a program you got lots more:
Because of the DEQM offer you earned gold after the fourth trip, and Platinum after the seventh, and with the respective 25% and 100% mileage bonuses you now have 53K+ miles in your account.
Citi AA MC sign up of 25K and a little bit of spending yields you closer to 80K miles.
SPG sign up and spending bonuse yields you 25k bonus miles, and you are now up to 105K miles.
You spend $30K per year on that SPG AmEx, and convert it over at a rate of 1.25 mi/$ due to SPG's bonus method, and now your have closer to $143K miles. (SPG purists bare with me, I know about the 20K issue, just trying to model the effective result)
And because you spent $30K on that SPG you are automatically granted Gold (second tier) status in the Starwood program.
Man, you did really well this year, and thats all without taking advantage of the more obscure opporunities, good job!
You see how this works? The program builds upon itself, like compounding interest.
Best of luck to you. And whatever program you go with, keep in mind that many of them offer a referral bonus. Keep your fellow FT members in mind for that.