Lets not get very sensitive about vendors here - I have been in the security industry for many years now and I do that for a living - network security, endpoint security, etc and despite having worked at multiple vendors and consultants as a security architect, I am not maintaining any vendor certifications (have been with Checkpoint/Nokia, Cisco as well as worked for some respectable security consulting organisations)
So keeping the vendors out, your network security device (firewall) is only as safe as its weakest link. In the case of a firewall software running on a commercially available operating system, the OS normally tends to be that weak link. No matter how much you harden the OS, there are still hundreds of vulnerabilities published every other day (every 2nd tuesday if you are a MS hotfix fanboy). Also a commercial OS like MS is not designed to handle packets and flows passing through it effectively, it is designed as an endpoint OS and no matter how good a firewall software you put on it, the limitations lie in the OS.
As far as autoenthusiast's advice goes, I would say he is spot on with the firewall architecture, yes you need a firewall with three interfaces - an inside, outside and dmz and yes you need to NAT your servers on the DMZ. This is the most secure design which they will teach you on any vendor neutral security architecture training.
With your architecture requirements in place. lets get back to vendors - Most firewall vendors realised the weakness of commercial OSs and decided to sell hardware firewall appliances (running a non-commercial OS - mostly a rewritten bsd/linux variant) instead of firewall software on MS/Solaris/RHEL/etc. Checkpoint realised this years ago and chose Nokia blades, juniper bought netscreen and ofcourse Cisco was always on hardware with their PIXes.
Then came some UTM firewall boxes, which combined every security function possible in one box. But generally speaking these were never good performers in anywhere but the really small offices - why - well for one they were dirt cheap (made the CFO happy) and secondly claimed performance figures on their datasheets which were never matched in their practical realworld numbers. The more functions you turned on (firewall, IPS, network AV, URL filtering, spam control), the more happier finance admins got, but on the flipside the more performance dropped (90% drops!!) and the more security admins cried their hearts out. Fortinet for one claims performance ASICs, which enhance firewall performance to 10gbps but turn out to be the reason for bad performance (200mbps when all functions are turned on - not because you need em but because you paid for em), as anything beyond firewalling is handled in software emulation by their el-cheapo asics. But then again who has a 200mbps ISP link. Besides for anyone hosting webservers, throughput hardly matters, the performance is measured in connections and connections/sec, as each http request is a new connection.
Now coming to your scenario, turning my vendor neutral hat off, since this is infact a best firewall thread, I would stop contesting on which is the best firewall (never ending discussion!!). The best firewall FOR YOUR REQUIREMENT will be a hardware appliance with good 24X7 support (not per incident support like MS), but good all round the year support at your beck and call. Cisco has stopped making PIXes, their firewalls are now called ASA 5500 series. There are models ranging from ASA 5505 (the cheapest - few hundred dollars including annual AMC) to the 10-20gbps ASA 5550 (which i am assuming you don't need

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Here is a datasheet to help you decide the right model for you
Cisco ASA 5500 Series Adaptive Security Appliances [Cisco ASA 5500 Series Adaptive Security Appliances] - Cisco Systems
and a video data sheet of the ASA 5505 if thats the model you need
Cisco ASA 5505 Video Data Sheet [Cisco ASA 5500 Series Adaptive Security Appliances] - Cisco Systems
Also to clear up any confusion - Cisco used to be a router and switch company, but if you think thats all they do, you are seriously out of touch with the industry - Cisco has been into security since a decade and also make Voice over IP phones and related technology, cable set-top boxes, linksys wireless devices, etc etc. Look at
Cisco Systems, Inc if you haven't yet!!
To top it all I am a Checkpoint fanboy (i was a checkpoint certified security expert), but I am not recommending them here as it is way too overpriced for your need and support is costed per incident. Besides their biggest hardware partner Nokia Enterprise Systems is up for sale (this is Nokia Cellular's firewall hardware division)
Thats all the advise I can give !!
Good luck with finding the best firewall (for your requirement

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