Fighter

As a fighter you can use only melee weapons. There are no ranged weapons in Torment that can be used by you. In fact the only ranged weapons in Torment are the crossbows that are used by Nordom, who can join your party later on in the game. As a fighter you also can not handle all melee weapons when you find them. You need to get some proficiency in using a weapon, which can be obtained by training. In Torment there are enough people who can train you in weapons. If you use a weapon for which you had no training then this will give you a negative adjustment to the ability to hit someone. When you start out you have only some proficiency in using daggers and small swords.

Other party members

You always start the game as a level 3 fighter and if you prefer close combat and swinging those melee weapons and there are some nice ones, than this is what you should stay.
When you look at the possible party members than they have the following classes:

Annah - Fighter/Thief
Dak'kon - Fighter/Mage
Fall-from-Grace - Priest
Ignus - Mage
Morte - Fighter
Nordom - Fighter
Vhaillor - Fighter

As you can see you can choose several fighters to join your party. This might be a reason not to stay a fighter. Also the first half of the game is not emphasized on fighting really and in the second half you have the party members that can fight with you. However be aware that each of the fighters listed above have there pro's and con's, of which some are listed below.

Annah - More a thief than a fighter, can not be hit very easily, which is good because she can not take a lot of hits. Because she is a thief she can use only knifes and should rely on magical knifes do do some serious damage.
Dak'kon - More a fighter than a mage, but good in both. Can use however only his own sword and no other weapons.
Morte - Can only use teeth as a weapon, although he can do some real damage with them. Because of his physical appearance he is difficult to hit by others.
Nordom - The only one that uses a ranged weapon. He is supplied with two crossbows that have an infinite amount of bolts. He can not use any other weapons and can therefor not be used in the front-line. The usage of ranged weapons is not so large in the game but can come in handy sometimes. Also, unless he uses some magical items he is relatively easy to hit. Because of that he should be watched over all the time.
Vhailor - Now this is a really big fighter. This one can handle the big melee weapons and he can swing them very good. He can take a lot of hits before he goes down and can carry a lot of weight. When you want to kill every bad guy who is walking around in the game then he is your partner to be. He can join your party in the second half of the game when all the serious fighting takes place. The downside of tagging him along is that he has some really funny ideas about justice and applying it. These ideas might not always be what you want and he might go around applying justice (which is the same as killing) when you want to let the 'victims' live. In this case Vhailor is unstoppable.

What to be ?

If you want to be a fighter then you get to swing those lovely melee weapons that are in the game. You could create an all fighter party, however I don't think that there is enough fighting in the game to have a lot of fun with such a party. But every now and then there is some serious fighting to do and because you are always the first of your party, it will hit you first. Being a fighter makes it a bit easier then.

Relevant Statistics

The following lists the statistic categories and there relevance to the fighter class in order of importance.

Strength - The most important statistic to have for a fighter
Dexterity - This makes you harder to hit
Constitution - Aids you in hitting your opponent and resources you faster
Charisma - As the leader you will need charisma to positively influence the reaction of others
Intelligence - Allows you to regain your memories faster and gives more dialog options
Wisdom - Let you recall memories.

Experience

During the game you can gain experience points. When the number of experience points that you or a party member has increased beyond a predefined threshold you, or one of the other fighters, can advance to a new level. This gains you extra hitpoints and can give you extra points that you can use to increase the statistics of one of the six categories.

At level 7 and level 12 you will get specialization bonuses.
L7: +1 Strength, train 4 extra classes in weapon proficiency.
L12: +1 Strength, +1 Constitution, train 5 extra classes in weapon proficiency.
If you use also other classes for the Nameless One then you will still only get two specialization's in total over (so maybe you never get the L12 specialization).

The table below shows the experience needed to advance to the next level and the number of hitpoints received.

To increase the maximum hit points a 10 sided dice is thrown. This results in the fighter getting 1 to 10 extra hitpoints. The dice is thrown upto 9 times, depending on the level. The fighter then receives the maximum value thrown.
Starting with level 10 the thrown number of the dices is increased with a fixed number.