Probably the most important parameter to consider, even ahead of the business valuation itself, are the terms of the investment contracts and/or shareholder agreements.
In many cases, as sophisticated investors (most of them these days) will want you to keep most of the risk, your control question might become moot.
For a start, minority shareholders (it can be you or your investors for that matter) can have minority protection clauses (veto powers for big decisions like additional funding, divestitures or extraordinary dividends) in the shareholder agreement or company bylaws.
Even if you still have control (>50%) right after an investment, founders (or angel investors) can be diluted if management misses their business plan projections (God forbid!) and milestone-based clauses in the investment contract are enforced.
Along the same lines, sorry to keep taking about worst case scenarios, most investors nowadays have anti-dilution provisions that can exacerbate the dilution of the founder round if there is a valuation "adjustment" in the future.
The later means that, to illustrate how anti-dilution provisions work, even if founders had a favourable Series A valuation, the Series A investors will have the right to adjust the original investment to a Series B valuation if the Series A turned out to be overvalued.
In conclusion, as other relevant comments in this posting, you may want to focus your attention on how much funding your business needs in order to grow... and also in a good corporate lawyer.
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