Pros and Cons for Tank
Pros: Good for GPR, Great for pushing mid/ fending away iron armor with teammate so they wont get the dias and let your potrusher get the dias, simply just a good kit, annoying for iron armor vs tank fights most likely tank will win with good pvp skills and its tanky too
Cons: so slow you can get 80 hit comboed by a fisting invis with blockhit/w-tap, easily notiecable and you get targetted means more deaths but this can be used to your advantage, you get slandered, not a lot of cons its a great kit
Pros and Cons for Enchanter
Pros: the best kit for potrushing if you are aiming for level 30 op armor and tools, you can pretend to be a "support" by giving your spyrushers/gold pick rushers efficiency II+ picks so they can get more nexus hits, especially when they have low ping and people think they are nuking (xD)
Cons: expensive, if you main vamp/hero/alchemist something like that you wont use enchanter kit that often and that 50k you can regret some of it. it dont have SHOVEL, means you can't chase people with dirt unless you make a shovel for yourself. also not that many cons, its a great kit
Conclusion:
Both kits are good, but tank can be useful more than enchanter. Overall buy tank first then enchanter (if you dont have any other kits you want to buy)