Hey folks, an opinion from the cofounder at BluSynergy, the customizable billing provider. Depending on your requirements and your desire to stay focused on your core product:
1. Rolling your own with a gateway like Paypal or Authorize.Net is often the easiest entry point (for US based startups at least), provided your requirements are not too complex. Especially if you are just getting started with an uncertain revenue prediction, there's little justification in trying to take on more sophistication. Do what's easiest for you - sling code or outsource to a SaaS billing provider. Unfortunately, the underwriting process is controlled by the credit card companies and tends to be cumbersome. No shortcuts there.
2. Once you've got a customer base, then you get the feel for the issues. Some examples: Mid-month upgrades/downgrades, chargebacks (customers disputing the charge directly with their credit card issuer), orders expiring, corporate customers wanting to pay by paper check, adding 1 time service charges to monthly bill, house credits or refunds, early termination fees, etc. Then you start thinking stuff like, gee, if I could notify my annual customers in advance I'd reduce a good deal of chargebacks and automate a lot of renewals...and so on... At this point you definitely want to consider either a SaaS billing solution or buying a platform and running it in-house (ya, we do both). And, now that you've got some volume, you'd want to switch CC processors for better rates. Let's hope you can get YOUR data back...
3. If your growth has continued past the above stage, then you want to be able to customize. Typical examples we see: commission and affiliate payouts, master billing (one consolidated corporate bill, a la your corporate telco+internet bill), custom payment retry logic (eg. ACH when paychecks are most likely to hit the bank), customer segmentation tactics (e.g. coupon codes for VIP customers to entice renewals), advanced billing models (eg. peak concurrent usage, or annual averaged billing), blacklisting bad cards, etc. The founders of BluSynergy spent two decades doing this kinda stuff for the big guys. Our specialty is that we designed the system from the ground-up to easily implement this level of customization (often less than a week) while still running in a cost-efficient multi-tenant model. And it's not just for the big guys anymore :)
Now see if any of this applies to your revenue strategy. For many, #1 above is still the best bet if your requirements are simple. There will be a migration effort when you get to stage 2, but at that point it's a "good problem" to tackle.