If you're a stealthy alien and can manage to sneak up on one or more marines, is it better to slightly injure the marines and retreat before they find you or kill you or is it better to rush in claws first, try your hardest to take one down but maybe die in the process.

Here's the arguements:

Kamikazi Tactic
Deciding what you do obviously depends on the situation. Your stage of evolution is probably the most important followed by what the marines are up to at the time you encounter them.
If an Onos see's a group of 2 or 3 marines or even more, he can probably just crush them there and then. You have a large pool of health and armor, so why not use it.
As a lower level alien, if the situation was bad such as your hive being attacked then you'd probably attack like a maniac even if it cost you your life.
Another reason to just Kamikazi is if you have nothing to lose. Anything above Skulk had to spend RP's to get to that stage and the further up the scale you get, the less you want to die. Because of this fact, lower level aliens are probably more willing to kamikazi for the sake of the team than higher levels.

Retreat Tactic
If you have little health left, or want to cause a distraction, or don't want to die then this may be a good tactic to use.
Upon finding your marine group, if they are posing no particular threat straight away then try firing in something to hurt them and retreat as fast as possible before they can realise what's going on.
Why not just go for a frag you ask? Well first of all, they either have to spend RP's to heal or they wander around weakened. (Not much RP's I know, but it may be vital at times and if you use this tactic enough it can be quite an annoying leech of funds)
The advantages of this is that they may be picked up on "Scent Of Fear" or another is that when they finally do begin to do something vital such as attacking a hive, they are already weakened and won't take as long to kill. I'd much rather face a group of 8 marines that are all on low health than 4 full health Heavy Armour guys.

If you're frag hungry and don't want to let othr people take your frags after you injured them, then try combining this tactic with a little stealth and cloaking. When you retreat to a safe distance, cloak and wait until they stop searching, just hope they DON'T find you. When they resume their normal duties repeat the process, hit em and run off again. YOu should be able to nibble away at their armour and health and maintain yours at close to full.

I've used the retreat tactic in other games, though I guess with guns I wouldn't call it that. I have always found it to be successful too. I really do love picking off people quickly and easily after they've spent a long time getting into your base, simply because you hurt them before they got there.

Don't forget that marines can be resupplied with health and ammo by their commander.

This means that an attack that did not kill at least one enemy, no matter how badly it hurt the rest, has to be called a failure.

If you're low on health and don't see how you could geek at least one, don't bother, get back to base, and heal yourself.

As a defense chamberless Skulk you'll die quite fast and might not even be able to get away at all, it's better to just run in and take out as many as you can before dieing.  Keeping the marines in base = more hives = win. If I have leap and carapace I’ll kill some and try and get out sometimes. When I’m playing a fade, lerk or onos I’ll retreat if I’m near death, it’s not worth the risk of losing all those resource points and I prefer carapace to redemption.

Some things to consider:

1) How much would dying cost?  As a skulk, you are "free" - it costs you nothing (or, at most, 6 RPs for 3 evolutions) to die.  If you're a Fade, it costs you 44 if you die - you'll probably retreat.

2) What's the danger level for your team?  Respawning takes a minimum of 10 seconds - if your hive is in grave danger, it may be better to pull back rather than waiting in the respawn queue.

3) What's the state of the rest of your team?  If you've got 3 other dead aliens, thats 30-40 seconds before you'll respawn if you die!  And if you're the only player between the marines and your hive, it may behoove you to stay alive, giving ground grudgingly, while you wait for backup.

4) What will your death/life accomplish?  The only use you can be to your team is killing a marine before you go down - if you don't kill one, then 2 RPs later, he's at full health again and ready to lay the smack down.  If you're not going to be able to kill anyone, pull back and wait till the odds are in your favor.

Well, El Bobbo CAN instil a form of Kamikaze in a Marine by parasiting him as I recall. Because basically, it's like slapping a veeerrryyy fatal 'Eat me' sign on his back. ^^;;

So if you wanna see kamikaze Marines, get your nostrils flarin'!