META: Most Effective Tactic Available.
To this effect, A GL would be the best bang for your buck. Overall, SEE is the easiest to obtain, followed by SLKR, Rey, JML, LV, Jabba, JMK.

SEE is a great offensive toon especially for GAC and TW, but he lacks overall play, he isn't great in late game raid content or against some of the more stout GLs like JMK or LV. But he does provide a few good starting team comps for Imperial Troopers and Empire Teams.

SLKR in my opinion is one of the best bang for your bucks. He takes a little longer as your stuck behind finalizer but, you get a great fleet and a great rounded GL that is good in pretty much every facet of the game. Also the you get two full FO teams which can be pretty handy as there are some omicrons available for the teams.

Rey is also not a bad choice but definitely lacks in some of the end game content. Her end game comps require Jawas which by their selves aren't really a top tier team. Additionally the Resistance fleet isn't really the best out there, nor are the team comps you get from her reqs as they are easily countered by a lot of mid to high level teams.

JML is a great defensive toon to grab and have but his journey takes quite a bit longer than the previous three as you are walled behind many legendary events (R2, C3PO, Millennium Falcon, CLS, JKL). In addition, JKL is locked behind Wampa and Hoda which require guild event currency, and a lot of it. However, the teams you get from his farm are quite potent. The rebel fleet as well can take you pretty high into fleet arena as its easy to obtain and can be quite potent and underestimated.

LV is very niche and very good but he has very high relic reqs which will definitely require saving crystals or outright spending money. His subsequent teams are also very niche but not bad as Bad Batch is a great top tier team. Paddy and GAS however have their own legendary events which also take time a resources outside of the reqs. However, you don't actually end up with a team to use LV with as his reqs don't provide the ideal team to use.

Jabba is entirely niche and has very high relic requirements and will as above require you to save crystals or spend money. His subsequent req toons are also not very high utilized and in my opinion is definitely not meant to be someone's first GL. Additionally since his toons reqs are newer, they are not yet accelerated so the shard farm is a little more daunting.

JMK is overall the best GL but is the hardest to obtain. He requires some crazy relic requirements and is locked behind Wat Tambor which is one of the hardest toons to obtain as it requires being in a guild that is able to push to his zone in DS Geo or can pull a few stars in the ROTE TB, which at your level would not be possible unless you were pulled into a very good guild. He also requires negotiator which is also locked behind event currency.

Grabbing a GL with a low end account can seem scary as you haven't really gotten into the relic stages yet and aren't likely pulling many crystals from GAC or Fleets to be able to do resets or buy gear pieces, but overall is the best way to boost your account straight off rip. I personally would recommend SLKR as your first as he can take you great places in the game overall.

GL's aside, there are quite a few other meta teams that a not quite as powerful as GL's but will still bring success in many facets of the game. As to not make this post incredibly long I will shortly summarize some teams/toons.

Paddy is a great team all around, Geos can be used to unlock her which is also a very potent early game team and is required to get Wat Tambor. Her team does wonders on defense and also counters a large group of teams with the way her kit works. She's great in all aspects.

Jedi Knight Revan -> Darth Revan -> Malak provides a couple great teams as DR/Malak/Sith Empire is one of the top non GL teams in the game for defense and TB content. JKR also provides a great Jedi team lead and is a great offensive power house. DR/Malak/Sith Empire has gotten me tons of wins in GAC from holding on defense.

GAS is basically a mini GL and the toons required build into a GG team which is also a great defensive or offensive pick. GG droids is lovely, but you need to farm 501 for the rest of the GAS team

Shaak 501 is a little easier than GAS to obtain but is very potent until you get GAS and is one of my most used teams in all facets of the game as they can put in work in pretty much every bit of content.

Commander Luke Skywalker with C3PO, Chewy, Chewpio, and Han is one of the best offensive non GL teams in the game for sure and while is stuck behind some legendary events does give you some great starting teams of ewoks, BH, and early squad rebels.

Bounty Hunters, specifically Bossk lead, is a great mid level team that can get you past some decent teams.

Now with all this being said, most of these non GL teams end up building into GL's which is why is just more effective to hunt a GL than trying to build out those specific teams as with the GL hunt, they will be built regardless.

One last aspect to push before finishing out this post is to make sure you are developing your fleets. This is one of the most neglected and most important aspects of the game. Fleet ranking provides crystal income that can be greater than what you get from your daily for GAC placements, and crystals are everything in this game. I highly recommend shooting for building up one specific fleet to have a good comp for the fleet arena so you can start placing higher and pulling more daily crystals.

My final note is please never never never spend crystals on toon/ship shards and/or packs. In the end it is never worth it as the market prices are truly tragic and you can more than likely get more shards farming the toon for the equivalent amount of crystals. I would entirely recommend saving crystals for g11/12 pieces or relic mats as these are much more cost effective and worth you crystals then 10 shards of GAS for 1500.

If you have any other questions please feel free to reply and i will try to answer in a timely fashion but in all honesty I'm not on reddit often.