I recently had a hard drive crash and lost my save code. I've since started putting the code online as well as on my laptop, but it sure is unfun starting over. What are some good strategies for leveling early?

Hello,

the fastest way to lvl is snatch a high lvl mate. Make medium and all team and let him own everything to lvl 120 with bonuswave . Perfect tower for that are a gattling or a owl or planar gate just repeat this step every 5 hours .

If you are solo hmm I think nature, ice is still a good starting combo.

Greetings

Chaosknight

The fastest way is, as StChaosknight mentioned, to team up with a high level mate and use him as an advantage on the easier difficulties and advance in difficulty when you feel you need more xp.
Pick Adventurer for increased item drop too, because more items for you and your teammate is equal to increased succes of getting something which might help you "win the game".

If you play solo you can try to speed run. (I would suggest you take the easy or very easy difficulty.) Pick any level 0 builder (I would suggest adventurer) level nature and ice with the main weight on nature. Than build some cacti (~3) and send wave after wave. Upgrade the cacti whenever you can and if the waves get to strong build more aoe/stun towers. (Forest Archer, Icy spires...) As carry tower I would suggest Furbolg, Stalker or Huntress. (with Huntress I managed to reach wave 148)

If you can build a magic mushroom, palm, dragon roost and more slow/stun towers.