you can do miner or fisher to get some starting monday. then i suggest you use tanner. BUt if you just want to stick with one bot id say to do miner becuase you can get decent money with that.
It may not be the best cash, but 80-99 mining is.. 170k gold ore or so. That's 40million and you can Living Rock Caverns which is fast exp. At the moment without a dragon pick, I am averaging (at level 83) 34k exp/h, 526 ores/h and 8.8 ores/m