That's really up to you to decide.
Personally I'd say earn in CEL as CEL potential is much higher than BTC.
Currently there are 97 million CEL available on the market and if you goal is hodl long term then CEL is a great way of acquire CEL before it goes up much higher.
Plus your CEL will also attract interest on your savings.
Why choose CEL
1) Upside potential is higher
2) More users everyday thus pushing up profitibiliy of Celsius and thus CEL token earnings via loans, crypto sales, interest income etc.
3) Very limited available CEL, it's finite.
4) If you ever want a loan should all crypto go higher, you can essentially pay it off with your interest.
5) Increased utility of CEL token in the future
6) Increasing demand for CEL by new users to reach higher tier of earning.
The inflection point is about a year out although we will likely see CEL prices move higher before the end of the year.
BTC is likely going to go x2 this year... CEL token could potentially go x10 with growth of the platfrom. So your earnings in CEL could be much more valuable.
Also we have seen in app holdings go up week by week.... remember the trend is your friend. Finally you could earn some CEL and always switch back to earning in kind to get some diversification.