Durable Carry - Opinions Needed

I don't recommend Chen if you're not familiar with microing, supporting and early ganking techniques (dust, etc.).
Also I can't recommend Lycanthrope as first jungler, cause his wolves die too quickly and require some jungling skills.

Enigma is very fun to jungle with, he requires basic microing (hero + eidolons), he farms lvl 6 early and can secure kills easily with it. Also if someone comes to gank him in jungle, his stun + eidolons can easily kill that brave one. Note - you can easily start jungling on hard camps.
Enchantress requires some more microing skills, but her skillset allows her to gank even without jungle creeps.
Lifestealer - I prefer to play him on lane, but in lower mmr you can find ppl afk farming in jungle for 30-40 minutes of game, and even after that time they are not able to carry sometimes. He's very good ganker (even after Open Wounds nerf) and good late game carry. Jungling with him basically means "lets attack that creep first and then my hero will automatically clear that camp".
Ursa - he's also better on lane with stun/slow babysitter, but his jungle is nearly the same as Lifestealer's one, you must farm for Tranquil Boots, then finish Vladmir's Offering with disassembling boots and go for Roshan.
Nature's Prophet is good farmer, jungler (he have 2 jungling techniques that I know - one with normal Treant's jungle, and second with maxing teleport and farming from cliffs), very fast pusher and can carry game if he get some items (Orchid, Desolator, Daedalus, Shadow Blade for escape...)

That's list of junglers I played and can recommend for starting jungler. They also fit in nearly every team composition - Enigma as initiator (tbh he's even better at counter initiating, when he can catch all 5 opponents, be careful if enemy have Rubick), Enchantress as hard carry (ye baby), Lifestealer as hard carry (even better when paired with Magnus or taxi heroes like Storm Spirit, Nyx Assassin), Ursa as hard carry (however he like to be paired with slows or stuns, cause he can be kited easily) and Nature's Prophet (as very strong pusher and semi carry).

What about Bloodseeker? He seems pretty awesome.

Also, by the Lifestealer thing, are you trying to say that even after afk farming for ages he still can't really carry? Sorry I'm a bit confused...

I never played with Bloodseeker, he is kinda russian hero :D
And about Lifestealer - in order to jungle with him effectively you need to understand carry and jungler roles - some people can afk farm for 30 minutes and still be ****, while good Naix will gank when possible or Infest is off cooldown, clear ancients etc. Jungler can't leave his team, at least not pub one.

Ah right, and do most games have a Jungler or is it like an optional role?

Most pub games have 2-1-2 setting, pro games have 3-1-1 setting (junglers on normal lanes if picked, for example mid Prophet, Naix on offensive tri lane [so much fun!]), sometimes 2-1-1 + jungler if Chen is picked. Ofc pubs also pick junglers sometimes, but nearly always they are just 30 min afk farmers and then they cry that team fed. And there is nothing worse than some1 saying "going jungle" with for example Skeleton King, and then he go on safe lane and say "lol jungling from lvl 3", it can't be called jungling.

So is Jungling a good role if I learn it well, or would I be better off learning how to play a conventional lane hard carry for Pubs and some premade games?

(I like the hard carry role) :D

It all depends on team setup if jungler can (and should) be picked or not, but there is nothing much you can learn about jungling, it's mix of all roles (support, carry, initiator, etc.). You should focus on playing on lanes, cause jungler is not stable role (I mean, you can't always pick jungler and most of the time you want to run tri lane if playing competitive), so stick with learning playing #1 hard carry, you can also find friend baby sitter to play with you and make your farm more effective. Leave jungling as situational and play it when you want/team picked 4 hard carries.

PS. I think that mid and solo hard lane are much more fun and skill-reliable (when you're left alone to show your skill and carry your team to win).

It's only worth learning to play a Laning Hard Carry if you have a decent Support or 2 (they shouldn't steal Last Hits, should harrass enemies, etc.) with you. Otherwise, you'll either want a Semi-Carry that can look after him/herself and get kills early on, or Farm in the Jungle.

If you're gonna Jungle, make sure that you emerge periodically to help your Team, especially if you can get kills or Towers, or prevent your enemies from doing so. You should also be careful about enemy Off-Laners coming into the Jungle to kill you or Ward the Neutral Camps (to see you and stop creeps from spawning - my favourite tactic against Lifestealer 8D).

There's nothing worse than a Jungling Lifestealer who sits in the Jungle for 30 minutes while the enemies Push and Gank their way to victory.

5 slot is the hardest role in the game (other than 1 slot captain) but 5 slot pays off. I found learning the jungle was fun but most games that I try to win a tri lane support is much better skill to know. pulls, stacks, smoke gank mid, push, ext.

I think this is the hardest because you are a "early game cary". Strong at the start and as time passes you become less effective. This make positioning very important because more often than not you can find yourself walking around with boots and a bracer.

Are there any heroes which can support early on in the game and then turn into a carry later? If so, are they worth playing?

Because I don't mind the support role, as long as the carry I'm playing with is good, and that is one heck of a thing to ask for in Pubs lol... So are there support heroes which turn into carries later on and therefore aren't so dependant on having a good carry to be paired with?

I guess what I'm really looking for is a role which isn't dependant on other people. Is there one?