It's a tough call, all three current WWI flight sims have their strong points over each other and all have their weak points compared to each other. It truly is a golden time for WWI flight sims, but also not an easy choice as you cannot get the ultimate total WWI package with any of them at this time. RoF is improving and adding more, OFF Phase 3 BHaH is working towards Phase 4, FE has recently been revamped to take advantage of the newer OS's and GPU capabilities and like all of TK's flight sims is very user modable. The safe bet is to get all three if you can swing it, thats what I did.

If you look at popularity, the number of users on the forums - here at SimHQ for RoF, at CombatAce for OFF and FE, it's a no brainer - it's RoF as it seems to be drawing the crowds, by a factor of 10 or more users most of the time.

A question about the activation : if I buy RoF, active it, play it... and change my PC in 6 or 7 years > will I have a problem concerning the activation (if we admit that the brand doesn't exist any more).

Arnauld, I would recommend First Eagles 2 from www.thirdwire.com for you.

Why? IMHO, it suits your personal situation best.

If you're only gonny fly one or two hours, maybe five hours a week, you will need many weeks to master RoF flying details, or to see trough a OFF3 campaign. Your system seems a tad weak to enjoy RoF in all it's graphical glory.

Both RoF and OFF, as far as I see, require a fair amount of familiarization and setup. One for the aircraft to become familiar with, the other for the campaign (and truth to be told, as splendig as OFFP3 is designed, it can't entirely hide the sub-par CFS3 engine running below it).

First Eagles 2 from Thirdwire, or even First Eagles Gold (which does not use DX10 graphic effects, but you only have XP currently, anyway) is a small game, quick to set up. It only has a handful of aircraft, but they are nicely detailed, and more would be available as mods if you care to look for them.

Current asking price in the TW store is 15 bucks, which makes it cheaper than both competitors.
https://store.thirdwire.com/store_p2.htm

But the best thing is really how simple it is to install and get started. All you should add is the modified terrain by Jan Tuma, available here:
http://combatace.com/files/file/10549-first-eagles-seasonal-tiles-by-jan-tuma/

In my opinion, OFF is perfect for people who know a lot of WW1 history, who know all the Aces and the Squadrons they flew in, and want to be part of that.
RoF is perfect for people who truly want to feel like flying those early aircraft, people who can debate online how this and that aircraft should perform, what it's flying characteristics should be.

First Eagles Gold would not fully satisfy either group. It has a semi-historic simple but effective campaign setup, and detailed, but not nearly as fully modelled flight behaviour as RoF.

But that's exactly the reason why IMHO it's perfect for people like you and me who want a complete package, minimal moding/setup required, and want to get in onto the WW1 action without first writing a scientific paper on WW1. The entire design concept of FEG will have you up and attacking enemies in minimal time. It's historic and realistic enough to provide atmosphere and a fair challenge in flying, but it's not so complicated that you can't enjoy it casualy.

And it has no copy protection. You just download the installer, and save that file somewhere. You don't need a disk in drive or activation.

Ok not a real WW1 flysim fan, then wait a while and get Olegs Battle of Britain!!!! See http://simhq.com/forum/ubbthreads.php/forums/91/1/Storm_of_War_Battle_of_Britain.html
and check the photo's

edit: Pat Wilson has made a campaign mode for RoF, now it is more a less in a beta stage but he is trying to make this like a RB3d campaign.

There is an interview with Albert and Jason on the front pages of SimHQ. Makes for some interesting reading re the immediate future of RoF and the long term strategy of the company

http://www.simhq.com/_air13/air_455a.html

Just My 2 Cents Guys, FE is a good casual game and as Colonel 131st has stated Detailed and mod enough to keep you happy. OFF is my most played game. The skill level is adjustable but living through a Campaign is a hard endeavor. The game is supported by forum and developer. Price is good, and its a stand alone game. Most of the aircraft are flyable and you don't have to buy each airplane.
The Campaign is like surviving a war all kinds of things go on. ROF is a great looking high detail operating flight program. A newer computer is a must as well as money for buying the airplanes. Then there's the must be online thing to play at all.

I play RoF without any internet connection! Just make the selection on-line or off-line play, thats simple. You need internet to do the free updates or flying on the net!

The way I look at it OFF:BH&H is a flight Simulation. The focus is on the complete air combat experience, the total war as fought in the air, and as realistically as possible. ROF:ICE is a Flight Simulator. The focus is on recreating the most realistic individual experience in the cockpit of a WWI combat aircraft. FE2 is a sim-lite version of both.

Looking at your specs (you'll probably be able to run ROF but will miss out on one of its biggest merits - the graphics), and considering that you won't play mutliplayer, I'd advise OFF.

Perhaps it's worth to wait, since ROF's upcoming career mode might tip the balance for single-player pilots, but OFF won't be a bad purchase and offers much bang for your buck.

By the time you get a new PC, who knows perhaps in two years, you might also be looking for a new flightsim experiece. By that time ROF will have evolved even further and you can switch to that.

Personally I prefer multiplayer, and while I will certianly enjoy the new career that's on the way, this makes ROf the only choice for me and I'm very happy with it. I'm sure I will be playing it for years to come. It's also a great community to be part of.