Short answer. It is your choice. A collection case may be commenced and tried where the plaintiff or any principal plaintiff resides, or where the defendant or any principal defendant resides, or where a nonresident defendant may be found, at the plaintiff's election.
What the law says
All other actions may be commenced and tried where the plaintiff or any of the principal plaintiffs resides, or where the defendant or any of the principal defendants resides, or in the case of a nonresident defendant where he may be found, at the election of the plaintiff.
Rule 4, Section 2 — Venue of personal actions. Read the full provision →
The plaintiff genuinely gets a choice here
This is a personal action — a suit to collect a debt does not concern title to real property — and the venue rule for personal actions gives the choice explicitly to the plaintiff: the case may be filed where the plaintiff or any of the principal plaintiffs resides, or where the defendant or any of the principal defendants resides, at the election of the plaintiff.
Once the plaintiff makes that choice and files, the case proceeds in that chosen venue unless the defendant successfully and timely challenges it as being genuinely improper.
Residence, not the transaction's location, is what matters
The rule ties venue to residence — the plaintiff's or the defendant's — rather than to where the debt was incurred, where the contract was signed, or where any related events took place. Someone deciding where to file should look at residence, not at the location of the underlying transaction that gave rise to the debt in the first place.
A nonresident defendant is handled differently
Where the defendant does not reside in the Philippines, the rule adjusts: the action may instead be filed where he may be found. This variant recognizes that a nonresident defendant may have no fixed Philippine residence to anchor venue to, so the rule substitutes wherever that defendant can actually be located within the country.
This gives the plaintiff a workable venue even when the ordinary residence-based rule cannot be applied.
Why this choice matters practically
Being able to elect venue lets a creditor file where it is genuinely more convenient for them, rather than being forced to travel to wherever the debtor happens to live. This is a real practical advantage in a collection case, and it is worth confirming that the case genuinely qualifies as a personal action under this rule, rather than one of the actions genuinely subject to a different, far more restrictive venue rule found elsewhere in the Rules of Court.