Which is a more common way, 10+ or 10 then + as superscript?

Solution 1:

10+ is sometimes used as a shorthand for 10 or more. Do not superscript the +.

A superscript + is normally only used for positively charged ions or particles: H⁺ for hydrogen ions, Na⁺ for natrium ions, K⁺ for potassium ions, Zn²⁺ for zinc ions, H₃O⁺ for hydronium ions, NH₄⁺ for ammonium ions, e⁺ for positrons, μ⁺ for antimuons.

Otherwise, superscripts are used:

• in mathematics, for exponents: 10⁶ is a million, 1 m² is a squared metre
• for footnotes
• for the abbreviations TM (trade mark) and SM (service mark) following a trade mark or a service mark
• for digits behind the decimal point or comma: $1.⁵⁰
• for the final letters of ordinals: 1^st, 2^nd, 3^rd, 4^th
• for the final letters of abbreviations that contain the first and final letters: M^lle for mademoiselle, M^r for monsieur or mister, D^r for doctor

Modern style guides advise against the use of superscripts in the last three points.

Solution 2:

I have not seen that usage of 10+ with a superscript as 10⁺.

Wikipedia says in Subscript and superscript

In English, most nontechnical use of superiors is archaic.

although I do still see (and sometimes use) superscript for ordinals like 10^th.

But it comes down to a matter of preferred style.