is sniper an all time, all map, all situation kind of class?

Sometimes being a sniper is really frustrating. Lately I've been practicing more and more sniper (almost 700 headshots already) so, no matter what game I'm in, I try to snipe, wich isn't easy with the sixaxis (i play on ps3). Many times, you're just being a less eficient player than you would be if you just built a sentry and a dispenser in a good spot. I have more time as sniper but much less points, compared to my spy, soldier and engineer ratings.

So, i kind of tend to only snipe when necessary or usefull. Are there permanent snipers that can be usefull to their team no matter what the conditions, maps, etc. are?

I snipe almost anytime any place. On PS3 I bet its far less useful though.

i usually just go sniper at the setup time, get a dot on the gate, and headshot people at the gate as they rush out
thats about as good as sniping gets for me x)

I tink snipers can always be useful. Either they are on defense (like most snipers on 2fort) or they attack together with a main combat class. I have experienced that they are great for taking out camping engis and their sentries. During a battle, many players don't notice a sniper standing in the back and preparing for a headshot.

But on the PS3, sniping is probably very difficult...

the only useful sniper is an expert sniper who plays the class ALOT and is proficient with the weapons. it's a very specialized class,
 imho

noob snipers can be of more use as a solly or demo or heavy (at least in pubs)

I've tried several "sensitivity settings" on the sixaxis for sniping. The main problem is that you rarely have enough control on the aim to make corrections on a shot. If you move just a little, you move too slow. If you push hard on the control, the aim will fly by the target. Also, you tend to move in straight lines (oponents dont). 
I usually lower the default sensitivity by two slots at least. But I'll try a cordless mouse tonight... who knows?

I dont think the sniper is always the best class to pick...if your enemy is very keen on spamming your battlements, and not giving you any room, you will do more for your team as a scout or soldier.    Unless you are snuts, then you just look in a direction and people will die. 
But there are major advantages of using a mouse over a controller.  

Even if you are a godlike sniper, there are times when it's just not feasible to be one.  The "meat and potatoes" classes (solly, heavy, medic, demo) are really the most important classes to have, and sniping is really just a support class.  If you have the key classes already, snipers are incredibly useful, as are scouts. 

It is the same with we spies.  Many times the battle needs a soldier much more than a spy/sniper.  I only play spy/sniper when the situation is right. 

*Good* sniper/spies are very effective on any map, at any time.  Snipers like Snuts/Durban, and spies like MisterStrum/Gman/Frozen/Dartagnan.  

I'm personally inclined to say that only the demoman, soldier and possibly medic are classes that are useable in any situation.  The rest of the classes are more specialized.   Engineers shine on CTF and assault maps, but do horribly on mirrored CP maps, conversely, the Scout is much more useful in any map where the Engineer cannot successfully establish himself.   The Heavy is a bit more well rounded, but can lag behind if a match ends up being faster paced.  The Sniper, like the Engineer, seems to do better on more static maps with less areas of focus (2 intel points rather than roaming active control points) but such is not the case.   These factors vary widely from map to map, considering map type, availibility of enclosed indoor spaces, wide open outdoor/indoor spaces, map layout and other factors. 

Another factor to take into consideration is the willingness of a team to cooperate ... medics, heavies and engineers are all classes that both derive and contribute greatly to orgainzed teamplay to a greater degree than other classes.  While all classes perform better when a team cooperates, the effect is magnified depending on which class you play.  You can still do very well as a sniper or soldier even if your team is disorganized or indavidualized, but being an effective engineer or medic becomes much more difficult under the same situations.

This is interesting ... somthing commonly seen on the TF2F (and I'm willing to wadger other servers) is the 'team stack' effect, where one side greatly outperforms another.   Part of this is due to genuine stacking of players familiar with each other, part of this is a collective difference in skill levels on teams.  However, take a hypothetical example of a match of all players of equal skill level on an indavidual level ... the team more willing to coordinate will generally win more often.  I'm of the opinion that the teamwork of a team, rather than the collective differences in skill, will have more of a 'teamstack' effect. I got to see this play out on SteamTV in a scrim between TF2F and another clan ... the opposing clan clearly had some incredibly skilled players, however TF2F was able to pull out a narrow win, despite loosing on point totals, simply because they were more coordnated (the skill differences were stark for two players in paticular, a demoman and a sniper).

It's frustrating for a player such as myself, who prefers a specialized class such as the Engineer, but I'm coming to realize that different maps may occasionally demand vastly different class layouts.