If you can put some figures into both the scenarios, it might make more sense as to which option is better.
So on one side, you have sell HDB and buy landed. You need to know how much your HDB can sell now, whats the purchase price of landed, whats the future monthly commitments, how long are you going to hold it and what capital gains are you looking for. Thereafter, what are you going to do once you have your capital gains.
On the other option, you need to find out the purchase price of the condo, how can you finance the purchase, what is the expected rental returns and financial commitments involved.
A word of caution is to always be prudent and conservative in your figures. Use a lower figure for sales and rental returns and higher figures for purchases.
Then, do a worst case and best case scenarios in the next 5-10years for both options so that you now have 4 potental outcomes. From there, the answer might become clearer.
You could do this yourself or if you wish an second opinion, you may contact me for an none obligatory discussion.